
Qass. 
Book. 






U. S. DEPARTMENT OF AGRICULTURE, 

BUREAU OF ENTOMOLOGY— BULLETIN No. 122. 

L. O. HOWARD, Entomologist and Chief of Bureau. 



THE ARGENTINE ANT. 



WILMON NEWELL, M. S., 

AND 

T. C. BARBER, B. S. A. 



Issued June 26, 1913. 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1913. 



/ 



/3^ 



Bui. 122, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate I. 




U. S. DEPARTMENT OF AGRICULTURE, 

'^ BUREAU OF ENTOMOLOGY— BULLETIN No. 122. 

L. O. HOWARD, Entomologist and Chief of Bureau. 



THE ARGENTINE ANT. 



WILMON NEWELL, M. S., 



T. C. BARBER, B. S. A. 



Issued June 26, 1913. 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1913. 



.^ 






B UREA U OF ENTOMOLOGY. 

L. O. Howard, Entomologist and Chief of Bureau. 
C. L. Marlatt, Entomologist and Acting Chief in Absence of Chief. 
R. S. Clifton, Executive Assistant. 
W. F. Tastet, Chief Clerk. 

F. H. Chittenden, in charge of truck crop and stored product insect investigations. 

A. D. Hopkins, in charge of forest insect investigations. 

W. D. Hunter, in charge of southern field crop insect investigations. 

F. M. Webster, in charge of cereal and forage insect investigations. 

A. L. Quaintance, in charge of deciduous fruit insect investigations. 

E. F. Phillips, in charge of bee culture. 

D. M. Rogers, in charge of preventing spread of moths, field work. 
RoLLA P. Currie, in charge of editorial work. 
Mabel Colcord, in charge of library. 

Southern Field Crop Insect Investigations. 

W. D. Hunter, in charge. 

W. D. Pierce, J. D. Mitchell, G. D. Smith, E. A. McGregor, Harry Pinkus, 
B. R. CoAD, G. N. WoLCOTT, W. A. Thomas, R. W. Moreland, C. E. Hester, 
engaged in cottoyi-boll weevil investigations. 

F. C. BisHOPP, A. H. Jennings, H. P. Wood, W. V. King, engaged in tick investi- 
gations. 

A. C. Morgan, G. A. Runner, S. E. Crumb, D. C. Parman, engaged in tobacco insect 

investigations. 
T. E. Holloway, E. R. Barber, engaged in sugar cane insect investigations. 
J. L. Webb, engaged in rice insect investigations. 

R. A. CooLEY, D. L. Van Dine, A. F. Conradi, C. C. Krumbhaar, collaborators. 
2 



!). OF D. 
JUL 11 1913 



LETTER OF TRANSMITTAL 



U. S. Department of Agriculture, 

Bureau of Entomology, 

Washington, D. C, January 2, 1913. 
Sir: I have the honor to transmit herewith and to recommend 
for pubHeation as Bulletin No. 122, of the Bureau of Entomology, 
a manuscript entitled ''The Ai-gentme Ant," by Mr. Wilmon Newell, 
formerly a collaborator, and Mr. T. C. Barber, formerly an agent of 
this bureau. 

The Argentine ant is an imported pest of great importance. It 
is unique among injurious insects of this country in the diversity of 
the damage that it causes. It is not only a household pest of the 
first rank, but it affects materially the interests of sugar planters, 
orange growers, and others. The territory infested by this ant is 
being rapidly extended. For all of these reasons it is important that 
there be placed on record a full account of the studies that have been 
conducted regarding it. 

The work upon which this manuscript is based was begun by Mr. 
Newell as secretary of the Louisiana State Crop Pest Commission. 
Later Mr. Newell continued the work as a collaborator in this bureau, 
and Mr. Barber, an agent of the bureau, but working under Mr. 
Newell's direction, added to the results obtained. 
Respectfully, 

L. O. Howard, 
Entomologist and Chief of Bureau. 
Hon. James Wilson, 

Secretary of Agriculture. 

3 



CONTENTS. 



Page. 

Introduction *. 9 

General considerations 10 

History and distribution *. 11 

Introduction into Louisiana 12 

Present distribution in the Southern States 14 

Occurrence and distribution in California 15 

Area of ultimate infestation 16 

Common name 18 

Means of dispersion 19 

Natural spread 19 

Flight 19 

Dispersion l^y streams 20 

Artificial dissemination 20 

Economic importance 22 

Systematic position 26 

Description of the species 27 

Resemblance to other ants 30 

Methods of study 32 

Establisliing colonies for study 36 

Life history 38 

The egg 38 

Period of incubation 39 

The larva 40 

Duration of the larval stage 41 

The pupa 42 

The worker pupa 42 

The male pupa 43 

The queen pupa 44 

The callow or teneral stage 45 

Time required for complete development 45 

The adults 46 

The worker 46 

Length of life 47 

The male 47 

The queen 48 

The virgin queen . . . . : 48 

The dealated, or fertile, queen 49 

The colony as a whole 51 

Seasonal history 51 

Winter colonies 51 

Summer colonies 52 

Compound colonies or communities 54 

5 



b CONTENTS. 

The colony as a whole — Continued. Page. 

Migrations 54 

General migration or dispersion • 54 

Migration to food supply 54 

Concentrating migration 54 

Divisional migration 55 

Nests or natural formicaries 55 

Underground nests 56 

Wet-weather nests or sheds 56 

General observations 57 

Aversion to light 57 

Sense of smell 57 

Sight '. 57 

Hearing 58 

Cannibalism ■ 58 

Sanitation 59 

Rate of travel 59 

Storage of food 60 

Relations with other Arthropoda 61 

Formicidse 61 

Coccidse and Aphididse 62 

List of Coccidse and ApHdidse attended by the Argentine ant 66 

Antagonism toward other insects 66 

The Argentine ant and the boll wee\il 68 

Beneficial aspects of the ant's activities 69 

Symbiotic relations 71 

Inquilines 72 

Natural control 72 

Natural enemies 72 

Insects and spiders 72 

Birds 73 

Experiments with Pediculoides 73 

Experiments with fungous diseases 75 

Low temperatures 76 

Floods 76 

Methods of repression 76 

Experiments with repellents 78 

Corrosive sublimate and ' ' ant tapes " 80 

Experiments with fumigants and contact in.secticides 81 

Experiments with poisons 84 

Control of the ant in residences 87 

Control of the ant in apiaries 88 

Control of the ant in orange groves 91 

Method of dissemination in the orange section 93 

Experiments in the orange groves 94 

Experiments with winter trap boxes 95 

Bibliography 97 



ILLUSTRATIONS. 



PLATES. 

Page. 

Plate I. Argentine ants upon a tea table Frontispiece. 

II A small colonv of Argentine ants as seen in one of the artificial for- 

nucanes - '^-' 

III. "Formicarium," or special insectary, constructed and equipped for 

the study of the Argentine ant 36 

IV. Immature stages of the Argentine ant - - - 40 

V. Wet-weather nest or shed, erected by Argentine ants during rainy 

weather ^" 

VI. Orange tree after exposure to Argentine ants for three seasons 64 

VII. Beehive on ant-proof hive stand, the latter resting upon a concrete 

block - 88 

VIII. Orange orchard dying as a result of infestation by the Argentine ant. 92 
IX. Batture of the Mississippi River 50 miles below New Orleans, over- 
grown with willows and heavily infested by the Argentine ant 92 

X. Siphon, pumping plant, and barrier ditch used in limiting the spread 

of the Argentine ant , 92 

XI. Bridges wliich the Argentine ant can not cross 92 

XII. Trap box and fumigating cover for destruction of Argentine ant 

while in winter quarters 96 

XIII. Orange grove in wliich campaign was waged against the Argentine 

ant— appearance of the grove after recovery 96 

TEXT FIGURES. 

Fig. 1. Map of Alabama, Mississippi, and Louisiana, showing counties in the 

Southern States which are infested l)y the Argentine ant 14 

2. Distribution of the Argentine ant in California 16 

3. Injury to the stand of sugar cane by the sugar-cane mealy-bug 

{Pseudococcus calceolarise) , wMch is attended by the Argentine ant.. 24 

4. Sugar-cane mealy-bugs on sugar cane 25 

5. Covering constructed by the Argentine ant to protect the mealy-bugs. . 26 

6. The Argentine ant, adult forms 28 

7. Artificial formicary or cage used in studying the Argentine ant 33 

8. Artificial formicary with parts assembled ready for use 34 

9. Entrance of artificial formicary shown in figures 7 and 8 35 

10. Argentine ant removing pupa of sorghum midge from a head of sorghum . 70 

11. Ant-proof hive stand, upturned, showing method of construction 90 

12. Ant-proof hive stand, sectional view 91 

13. Ant-proof liive stand, from above, showing construction 92 

7 



THE ARGENTINE ANT. 



INTRODUCTION. 

The Argentine Mit (IridomyrMex humilis Mayr), which is made the 
subject of the present paper, is the first among the Formicidse to attain 
the front rank among injurious insects in the United States. In its 
field the Argentine ant is hot excelled m destructiveness by even the 
gipsy moth, the boll weevil, or the San Jose scale. Though this ant 
is limited as yet to comparatively small areas, the observations and 
experience of the authors fully convince them that future years will 
see this insect steadily invading new territory and forcmg its depre- 
dations upon the inhabitants of all southern California and most of 

the Gulf States. 

The present paper aims to present, m as concise a manner as possi- 
ble, the principal results of five years of almost constant observa- 
tion and experiment by the senior author at Baton Kouge, La., and m 
the orange-growing section of the same State, together with observa- 
tions made by the junior author at New Orleans in connection with 
his investigations of sugar-cane insects. 

The junior author has prepared in their entirety the portions deal- 
ing with the ''Area of ultimate mfestation," and the " Relation of the 
ant to Coccidje and Aphididae," and to him is also to be credited the 
unportant discovery that mating of the queens may occur withm 
the formicary or nest of the colony. The remainder of the paper, 
except where otherwise noted, is compiled from the notes and records 
of the senior author. 

In the tedious work which accompanied the determination of the 
ant's life history, from 1907 to 1910, much assistance was rendered 
by the young men associated with the senior author in the work of 
the Louisiana State Crop Pest Commission, particularly Messrs. 
Harper Dean, A. H. Rosenfeld, G. A. Runner, M. S. Dougherty, 
G. D. Smith, and R. C. Treherne. 

The writers are under obligations to Dr. W. M. Wheeler, of the 
Bussey Institution, Harvard University, for permission to use his 
redescription of Iridomyrmex Jiumilis and for his kmdness in reviewing 
the paragraphs upon "Systematic position" and "Resemblance to 
other ants." 

Our thanks are also due to Messrs. R. S. Moore and John Meyer, 
extensive orange growers of Louisiana, for their liberal cooperation 

9 



10 THE AKGENTINE ANT. 

and assistance in experiments carried out in the infested orange 
districts. 

GENERAL CONSIDERATIONS. 

Twenty years ago the Argentine ant was first noticed in New Or- 
leans, La., by Mr. Edward Foster, reference to whose interesting 
account of the ''Introduction of Iridomyrmex humilis Mayr into New 
Orleans" will be found on a subsequent page. The species had 
doubtless been introduced years before that time, but was gathering 
strength and establishing itself for a considerable period before its 
numbers became sufficient to attract attention. Mr. Foster men- 
tions it as occurrmg in 1891 in ''fan* numbers." Since then it has 
increased from a few scattered and apparently insignificant speci- 
mens to armies and hordes numbering myriads of individuals. It 
has spread from a few blocks on the water front of the Mississippi 
River over practically the entire city, and has sent out vast numbers 
of colonists for hundreds of miles along the railways and waterways 
radiating from New Orleans. These pioneers have succeeded in 
founding scores of communities of more or less importance in the 
smaller cities and towns. Each of these communities is in turn 
furnishing its quota of migrants, and these are extending the affected 
territory in all directions from the original source of infestation. 
Thus, instead of the dispersion being from one source only, it is now 
taking place from hundreds of different points. From an unknown 
and little noticed insect this ant has developed into one of the fore- 
most household pests in the world, and its ravages affect, directly or 
indirectly, the majority of the crops grown in the South. Former 
indifference to its movements has given way to concern at its approach, 
which, in the orange belt at least, means heavy depreciation in the 
value of property. 

Continuous study for several years has served to enlighten us on 
most of the salient features in the life history and economy of the 
species. A considerable number of poisons and repellents have been 
tested and have given good results. Methods of isolating, ditching, 
and winter-trapping have been devised, and have proved their prac- 
tical value in large experiments under field conditions. 

Just how much territory this ant will ultimately infest we can not 
foretell with accuracy from the data at present available. It is 
quite safe, however, to venture the opinion that the species will 
eventually spread over a considerable portion of the Southern States — 
certainly over all of the orange and sugar-cane belts, and perhaps over 
all of the cotton belt. In California it is likely to cover the territory 
corresponding in temperature to the belts mentioned for the South, 
which will include the belts occupied by oranges and other tender 
fruits. 



THE AEGENTINE ANT. 11 

HISTORY AND DISTRIBUTION. 

As stated on another page, this species was first described by Dr. 
Gustav Mayr from specimens collected near Buenos Aires, in Argen- 
tina. It is also included in the list of Argentine ants by Dr. Carlos 
Berg.^ Its occurrence in the Argentme Republic is therefore unques- 
tioned, and that Argentina is its native home is also borne out by the 
fact that it does not appear to be generally a pest of importance in that 
country. Dr. F. Lahille, of the Argentine department of agriculture, 
in a letter to the senior author, states that it ''is uncommon in 
Buenos Aires and m Argentma generally, where it does not cause 
annoyance or trouble of value." Mr. Arthur H. Rosenfeld, formerly 
associated with the writers m entomological work in Louisiana and 
now located at Tucuman, Argentina, writes that he has been unable 
to find the species there. Rev. E. Wasmann, S. J., states that this 
ant '4s a native of Brazil and Argentina," and Rev. Albert Biever, 
S. J., of Loyola College, New Orleans, whose careful studies of 
this species are mentioned on other pages, has corresponded with 
various priests in Brazil and Argentina, with the result that he finds 
that this species is a serious pest in parts of Brazil and evidently in 
Argentina also. For example, in a letter to Father Biever, Rev. J. 
Ferol, S. J., of the Colegio del Salvador, Buenos Aires, writes: 

The ants {Iridomyrmex humilis) of which your reverence makes mention are of no 
utility whatsoever, but on the contrary are voracious and destructive. Of means 
employed to destroy them the most effective, according to information given me, is 
the use of an instrument and ingredient of which inclosed herein I send a prospectus 
and instructions concerning its use and functions. 

Forel ^ mentions its occurrence in collections from the States of. Sao 
Paulo and Rio Grande do Sul, in Brazil. Wheeler ^ also mentions 
its occurrence in that country. Dr. Lahille also states that the 
Argentine ant occurs in Uruguay and is "especially common in 
Mercedes and Montevideo," cities not far removed from Buenos Aires. 

According to Stoll " and Wheeler ^ the Argentine ant, after its 
accidental introduction into the island of IMadeira, entirely extermi- 
nated another ant, Pheidole megacephala Fab., which was itself an 
introduced species that had exterminated the native ants before it. 

In 1907 M. N. Martins ^ recorded the occurrence of this ant in 
Lisbon and Oporto, Portugal, and gave a vivid account of its ravages 
in those cities and their environs. 

1 Enumeraci6n sistematica y sinon^mica de los Formicidos Argentinos, ChUenos y Uruguayos. 1890. 

2 Ameisen aus Sao Paulo (Brasilien), Paraguay, etc. Verhandlungen der k. k. zool.-bot. Ges. in Wien, 
1908. 

3 Entomological News, January, 1906, p. 24. 

< Zur Kenntnis der geographisehen Verbreitung der Ameisen, Mitth. Schweiz. Ent. Ges., vol. 10, pp. 
120-126, 1898. 

5 Ants: Their structure, development, and behavior, p. 154, 1910. 

« Une fourmi terrible envahissant I'Europe {Iridomyrmex humilis Mayr). Broteria Revista de Sciencias 
Naturaes, vol. 6, pt. l, pp. 101-102, 1907. 



12 THE ARGENTINE ANT. 

In 1908 Prof. C. P. Lounsbuiy recognized this ant in Cape Town, 
South Africa, where it had already become a household nuisance and 
had displayed its usual role of attending mealy-bugs and other insects. 
The general belief in Cape Town, according to Prof. Lounsbury, was 
that the pest had been introduced through the medium of forage, 
large quantities of which were imported from Argentina during the 
Boer War (1900-1902) and stored in Cape Town. 

In July, 1910, the late Edwyn C. Reed, of Concepcion, Chile, in a 
letter to the senior author, reported the occurrence of the species in 
that country in large numbers. 

In 1908 ants collected by Mr. J. Chester Bradley, of the University 
of California, were identified as 1. liumilis by Dr. W. ^I. Wheeler. 
Immediately following tliis discovery Prof. C. W. Woodworth, of the 
California Agricultural Experiment Station, visited the authors' 
laboratory at Baton Rouge, La., for the purpose of becoming familiar 
with the methods used in studying the insect and with the information 
which had been gathered concerning it up to that time. On his 
return to California he published a brief circular ^ concerning its 
occurrence in that State. 

From the foregoing it is readily seen that during the past few years 
this ant has thoroughly established itself, as a nuisance of the first 
order, on four continents, and, owing to the readiness with which it is 
disseminated through the ordinary channels of commerce, there 
seems little reason for supposing that it will not eventually invade 
all of the semitropical countries of the globe. 

INTRODUCTION INTO LOUISIANA. 

As with most imported species, the original time and place at which 
a foothold was obtained by the Argentine ant in Louisiana must be 
largely conjectural. However, we are able to conjecture with rather 
strong circumstantial evidence to guide us. Not only does the tes- 
timony of inhabitants indicate New Orleans to be the original starting 
point of this species in the South, but its enormous numbers and the 
extent to which it has exterminated other species of Formicidse con- 
firm the opinion that it has been in New Orleans longer than else- 
where. 

Mr, Edward Foster,^ of the editorial staff of the New Orleans 
Daily Picayime, has given us the earliest record of its occurrence in 
New Orleans. He noted it in 1891 in St. Charles Avenue, 9 
squares from the river and 12 from Canal Street. It was then 

1 The Argentine ant in California. Cal. Agr. Exp. Sta., Cir. 38. August, 1908. 

2 The introduction of Iridomyrmex humilis into New Orleans. Joum, Econ. Ent., vol. 1, No. 5. pp. 
289-293, October, 1908. 



HISTOEY AND DISTRIBUTION. 13 

present in ''fair numbers." At that date it was very scarce in 
Audubon Park and below Canal Street, but was present in considerable 
numbers between Magazine Street and the river. 

''Five or six years later" he found it in St. Peters Avenue, near 
St. Charles, but it was not abundant. This is about 40 squares 
north and west from the point on St. Charles Avenue first referred to 
by Mr. Foster. 

In a personal letter to the senior author, ]\Ir Foster writes as 
follows : 

I have known the species since 1891 . At that time it was a rarity in Audubon Park, 
but was very common in the section immediately above Canal Street. Below Canal 
Street it was not at all plentiful. The boundary of the nuisance then was virtually 
from Magazine Street to the river. The coffee ships from Brazil, I understand, have 
always landed about where the wharves are now situated (on the river front, adjoining 
the area above mentioned), but from what we know of the spread of msect nuisances 
the first batch of immigrants must have come in years before I came across their 
descendants. 

Mr. E. S. G. Titus,* quoting Mr. E. Baker, former superintendent of 
Audubon Park, states that in 1896 "they extended over but a small 
area, reaching approximately from Southport docks to CarroUton 
Avenue and from the river bank to Poplar Street," and that "in 1899 
they were first noticed in Audubon Park. " This area, from Southport 
to CarroUton Avenue, is located about 5 or 6 miles northwest of the 
area between Magazine Street and the river, noted by Foster to be 
well infested as early as 1891. Mr. Baker, therefore, had not been 
familiar with the original area of heavy infestation, but merely noted 
the species after it had invaded the part of the town where he resided. 
Mr. Titus's information that the species was first noted in Audubon 
Park in 1899 was of course secured from citizens, who failed to note 
the ant until it had reached prodigious numbers in the same place 
that Foster had found it a "rarity" in 1891. The dissemination to 
Audubon Park was undoubtedly from the heavily infested area 
between ^lagazine Street and the wharves already referred to. 

The distribution of the species in 1904, as given by Air. Titus,^ was 
as follows : 

Across the river in Algiers and adjoining small settlements; at West End, Spanish 
Fort, and Milneburg, summer resorts on Lake Ponchartrain ; Bay St. Louis, Miss., a 
summer resort between New Orleans and MobUe; along the Texas & Pacific Rail- 
road at Donaldsonville, Cheneyville, and Alexandria; along the Southern Pacific at 
Thibodeaux, Schriever, Houma, Berwick, Morgan City, Franklm, New Iberia, and 
La Fayette, and at Opelousas. 

There is every reason for supposing that this ant was introduced 
into New Orleans by means of the coffee ships which have for years 

1 Bui. 52, Bur. Ent., U. S. Dept. Agr., p. 79, 1905. 2 ibid., p. 82, 



14 



THE ARGENTINE ANT. 



passed back and fo*rtli between that city and Brazilian ports. This 
view is supported by the fact that large numbers of the ants were 
first noticed in the vicinity of the wharves where these ships unloaded 
their cargoes and also by the fact that these ships have been the only 
means of regular communication between New Orleans and the 
countries in which the ant is indigenous. That this and other species 
of ants are actually transported on ocean-going vessels has been fre- 
quently observed. Thus in July, 1911, the senior author, while a 
passenger on one of the largest coastwise vessels between New Or- 
leans and New York, found colonies of tliis same ant occupying pro- 
tected situations in the woodwork of the steamer. Dr. W. M. TVTieeler 
also writes us that while returning from Guatemala aboard a fruit 




Fig. 1. — Map of Alabama, Mississippi, and Louisiana, showing counties in the Southern States which are 
infested by the Argentine ant, according to the authors' records. (Original.) 

steamer in January, 1912, he found it infested with another common 
ant, Prenolepis longicornis Fab. 



PRESENT DISTRIBUTION IN THE SOUTHERN STATES. 

The area in the Southern States within which the Argentine ant 
is known to occur at present extends from Montgomery, Ala., to 
Lake Charles, La., a distance of about 380 miles east and west; and 
from Delta, La., to the mouth of the Mississippi River, a distance of 
about 250 miles north and south. (See fig. 1.) This section is not 
uniformly infested, but contains a great number of infested areas of 
more or less importance, ranging in size from man}^ square miles of 



HISTORY AND DISTRIBUTION. 15 

occupied territory, as illustrated by the infestation at New Orleans, 
to areas where the ants are so scarce that one not accustomed to their 
habits would fail to discover them. The latter condition prevails at 
present in Mobile, Ala. The only places remote from railroads 
where they have been discovered are upon the banks of the Missis- 
sippi River below infested localities. Their presence in such loca- 
tions is easily accounted for by supposing that they have been carried 
thither on driftwood, which, carrying numbers of ants from infested 
places farther up the stream, has become stranded on the river banks, 
thus establishing new foci. In all other cases the infested territory 
is on a raih'oad, and usually on a main line running out from New 
Orleans. For example, nearly every town along the Southern Pa- 
cific Railway between New Orleans and Lake Charles is infested, and 
the same statement applies to points on the Louisville & NashviUe 
Railroad between New Orleans and Mobile. 

OCCURRENCE AND DISTRIBUTION IN CALIFORNIA. 

The first specimens of the Argentine ant observed in California 
were collected in 1907 by Mr. J. Chester Bradley, at that time an 
assistant in the entomological department of the University of Cal- 
ifornia. The identity of the specimens was not established until 
1908, when Dr. W. M. Wheeler found them to be Iridomyrmex humilis 
Mayr. 

As soon as the dangerous nature of the pest was known, Prof. C. W. 
Woodworth took steps to make a study of the species along the same 
lines as was being conducted in Louisiana at that time, and as a result 
of his preliminary work he issued a warning circular ^ to the public 
in August, 1908. In this circular he gave a brief outline of the 
habits of the ant and reported the following localities as infested: 
In the central portion of the State, East Oakland, Alameda, San 
Francisco, San Jose, Cupertino, and a point near Campbell; in the 
southern part of the State, Los Angeles, Azusa, and Upland. 

In 1910 Prof. Woodworth i)ublished another small buUetm ^ giving 
the results of his two years' study of the insect. In this paper the 
infested territory was more clearly defined, and was estimated as 
consisting of a total area of 5,000 acres. About twice the area was 
reported infested in 1910 as in 1908, owing to the discovery of a few 
new colonies and the natural spread of the ones first discovered. 

Our information as to the extent of the infested area in California 
(see fig. 2) has been obtained principally through the kind offices of 
Mr. Ralph Benton, of the California Agricultural Experiment Station, 
and Mr. P. E. Smith, of Santa Paula, Cal., as well as from the publi- 

1 The Argentine ant in California. Cal. Exp. Sta. Cir. 38, Berkeley, Cal., August, 1908. 
s The control of the Argentine ant. Cal. Exp. Sta. Bui. 207, Berkeley, Cal., October, 1910. 



16 



THE AKGENTINE ANT. 



cations by Prof. C. W. Woodworth, already referred to. All of these 
persons agree that the following California points are infested: Ala- 
meda, Azusa, Berkeley, Byron Hot Springs, Campbell, College Park, 
Cupertino, Fruitvale, Los Angeles, Melrose, Oakland, Riverside, San 
Francisco, San Jose, Stockton, and Upland. 






— ■ -. ■ f — • — 1» 



' S T A .-' 
7 \0 






U- 



I. A s s e 



B jT)-£ 






^Sojtfo ^\hapa\ 






>0 



;%^\ 













o"^ 






Ill/Ins^"- 



•^^f^rs. 






% 






Fig. 2. — Distribution of the Argentine ant in California. From data furnished by Messrs. Ralph Benton 
and P. E.Smith. (Original.) 

AREA OF ULTIMATE INFESTATION. 



Up to the present we have no exact data to indicate the final limits 
of the area which may become infested by these ants. They appar- 
ently thrive as well at Delta, La., at an elevation of 87 feet, as they 
do near the mouth of the Mississippi River, 300 miles to the south 
and almost at sea level. They seem to be little or not at all affected 



HISTORY AND DISTRIBUTION, 17 

by the variation in the amount of precipitation annually as between 
different localities, for they seem to flourish as well at San Jose and 
Los Angeles, CaL, with average annual rainfalls of 14.8 and 15.6 
inches, respectively, as they do at New Orleans, La., where the aver- 
age annual rainfall is 57.6 inches. The range of temperature to 
which they have adapted themselves at different points does not 
vary so greatly, but is nevertheless considerable. They have suc- 
ceeded in establishing themselves at San Francisco, Cal., where the 
mean annual surface temperature is 56° F., or 13° cooler than the 
mean annual surface temperature at New Orleans, La. 

If we assume that the Argentine ant is unable to persist in local- 
ities where the mean annual temperature is below 55°, we will find 
that the isotherm of this temperature extends almost up to Columbus, 
Ohio, and past St. Louis, Mo., and wiU include over one-third of the 
United States, or more than 1,000,000 square miles. It is very 
unlikely, however, that this neotropical species will be able to endure 
the cold winters in the northern parts of this area. It will probably 
be more nearly correct to assume that its advance will be checked 
when it reaches the minimum isotherm of zero, or, in other words, 
where the thermometer drops to zero or below during the as^erage 
winter. On constructing this isotherm we find that we have the 
following area within the United States liable m the course of time 
to infestation by the Argentine ant : 

Starting at the Atlantic coast line; one-half of North Carolina, 
one-half of South Carolina, one-half of Georgia, Florida, a portion of 
Alabama, one-third of Mississippi, most of Louisiana, all of lower 
Texas, a corner of New Mexico, one-half of Arizona, a little of Ne- 
vada, practically all of California, and a coastal strip through Oregon 
and Washington. This would extend the infestation into fourteen 
States, more or less, and is undoubtedly a very conservative predic- 
tion, as already the ant is established at one point. Delta, La., which 
is above tliis line. 

In spite of these considerations we are stiU in the dark as to the 
altitudes at which this insect will thrive, and it may be found later 
that altitude will severely limit the distribution of this species, as it 
does that of many other insects. Table I gives the elevation and 
climatological data for a number of infested points in the United 
States, and from this table it will be noted that the elevation of 
points now infested varies from sea level to 338 feet. 

The climatological data given in Table I are taken from BuUetin Q, 
Weather Bureau of the United States Department of Agriculture, 
1906, entitled "Climatology of the United States," by Alfred Judson 
Henry. 

75508°— Bull. 122—13 2 



18 THE ARGENTINE ANT. 

Table I. — Data concerning various towns infested with the Argentine ant. 



Name of town. 



Montgomery, Ala. 

Mobile, Ala 

Vicksburg, Miss . . , 

Meridian, Miss 

Hattiesburg, Miss. 

Biloxi, Miss 

Alexandria, La. .. 
Baton Rouge, La . 

Delta, La 

Lake Charles, La., 
New Iberia. La . . . 
New Orleans, La.. 
Sacramento, Cal. . 
San Francisco, Cal 

San Jose, Cal 

Los Angeles, Cal. . 



Eleva- 
tion. 



Feet. 

196 

11 

229 

338 

154 

24 

77 

62 

87 

22 

15 

8 

29 

28 

95 

287 



Mean 
annual 
temper- 
ature. 



'F. 



(') 



Absolute 
maximum 
temper- 
ature. 



(') 



107 
102 
101 
104 
103 
100 
109 
103 
) 

103 
101 
102 
108 
100 
104 
109 



Summer 

maximum, 

mean. 



(') 



Absolute 
minimum 
temper- 
ature. 



- 1 

- 1 

- 6 

- 1 
1 
2 
2 



(■) 



AVinter 

minimum, 

mean. 



(') 



Mean 
annual 
precipita- 
tion. 



Inch ex. 
50.8 
62.1 
53.8 
53.4 
48.1 
61.3 
54.9 
54.6 

53.3 
53.7 
57.6 
19.9 
22.5 
14.8 
15. 6 



' Records not available. 



Note. — " Summer maximum, mean "=the average of the total maximums for June, 
July, and August. " Winter minimum, mean "=the average of the total minimums 
for December, January, and February. 



COMMON NAME. 

The name "Argentine ant" was first used by the senior author for 
this species in 1908, when the public was on the point of accepting 
the name "New Orleans ant." The permanent use of the latter 
name would manifestly have been unjust to the Crescent City, for 
that city was in no way responsible for the introduction of the pest. 
As stated on preceding pages, this ant was originally described from 
specimens collected in Argentina, South America, and up to the 
present time we have no reasons for not believing that this is one, at 
least, of the countries in which this ant is native. The naming of 
this ant after the country from which it was first described is by no 
means without precedent. Many other common insects, such as 
the San Jose scale, American cockroach, Colorado potato beetle, 
Mexican cotton-boll weevil, etc., have received their popular names 
in the same manner. 

Various common names have been suggested from time to time, 
among them "crazy ant," "tropical ant," "pernicious ant," etc., 
but all have the disadvantage of being as applicable to other species 
as to Iridomyrmex Jiumilis and none of them is distinctive. 

The term "Argentine ant" has been readily accepted, alike by 
entomologists and the press, is concise, and not likely to be confused 
with similar names; hence we believe it to be as good a name as can 
be adopted. 



THE ARGENTINE ANT. 19 

MEANS OF DISPERSION. 
NATURAL SPREAD. 

Under strictly natural conditions, the rate of dispersion of Argen- 
tine ants is very slow. Owing to their intensely social habits they 
spread but slowly from a locality until the number present becomes 
excessive for the food supply or unless adverse conditions, such as 
flooding, occur which compel them to seek fresh locations. They 
will then spread in all directions, but will go little farther than is 
necessary to give them sufficient foraging area to insure the food 
required. However, if a large food supply is discovered at a con- 
siderable distance from the colony, a heavy trail of workers will 
soon be formed between the food and the nest, composed of many 
thousands of tiny insects, each busy carrying a load of the coveted 
material back to the nest or going out for another load. Sometimes 
they will construct a -new nest in the neighborhood of the food sup- 
ply, and to this they will transport a number of pupae, larvae, and 
eggs from the parent nest. In the course of a day or so this new 
colony mil be thoroughly established, wdth a full supply of queens, 
workers, and immature stages, and will then be capable of supporting 
itself and increasing in numbers without assistance from the parent 
nest. 

Under normal conditions it is likely that the rate of spread does 
not amount to more than a few hundred yards each year. "When 
food is plentiful, a well-traveled road or a paved street may restrict 
the spread for a considerable period, but when any much-desired 
food supply, such as the excretions of aphides or scale insects, is to be 
reached, nothing short of running water proves an effective barrier. 



It is possible, but scarcely probable, that the queens may aid the 
natural dispersion by means of flight, but there are several reasons 
why this is doubtful. One of them is that the flight itself is a very 
uncertain event, as during the five years that these ants have been 
studied in Louisiana only one general flight has been observed. It 
has been established that the young queens can mate in the nest 
without taking a marriage flight at all, and apparently this is what 
usually takes place. Even should a fertilized winged queen fly or 
be transported by the wind to any considerable distance from the 
ant-infested territory, it is very doubtful whether any eggs she might 
lay would ever hatch. The queen has never been observed assisting 
in the slightest degree with the rearing of the young in the nest, nor 
have we succeeded in getting eggs to hatch when they were not 
cared for by the workers. As the workers are never winged, the 
queen would necessarily be alone, and it would be very unlikely 



20 THE ARGENTINE ANT. 

that the queen would develop the instinct of attending to and caring 
for tlie eggs, larvae, and pupae in succession for several months. 
Also, the queens are quite helpless and appear to be entirely incapa- 
ble of defending themselves against other insects. The writer has 
observed a Cj[ueen ant being captured and bound by a minute spider, 
considerably smaller in size than her own head, without making 
the least attempt to struggle. It therefore seems improbable that a 
defenceless queen could maintain herself in a hostile country for 
several months without the assistance of workers. 

Furthermore, we have several times kept Argentine ant queens 
isolated in small nests, sometimes singly and sometimes in groups, 
but have never yet succeeded in hatching eggs in these nests, or in 
rearing larvae to the adult stage. 

The fact that ditches of running water have proven sufficient bar- 
riers to prevent the spread of the species in orange groves appears to 
disprove the theory that queens returning from the nuptial flight can, 
without the assistance of workers, establish new colonies. 

DISPERSION BY STREAMS. 

As previously mentioned, driftwood is probably the most important 
agency in the natural dispersion of the Argentine ant. Along the 
Mississippi River, below the infested territory, we find a considerable 
number of larger or smaller colonies of the ants, and in places the 
batture ^ will be infested for miles, with practically no ants inside the 
levee. This can only be accounted for by ants floating down the 
river upon driftwood from infested localities. The river banks are 
covered with logs, more or less rotten, which have stranded during 
high water. In the infested territory these logs are found full of 
ants in all stages in enormous numbers. During high water some of 
these logs drift and lodge alternately, gradually working clown the 
river, and distributing colonies in their wake. 

The writer has several times seen complete colonies of ants on a 
floating log, unable to escape. All that was required was a little 
further rise of the water to start them down the river, with their 
cargoes of ants. 

ARTIFICIAL DISSEMINATION. 

Unquestionably the main distributing agent of the Argentine ant 
is man himself, by means of railway trains, boats, and other vehicles 
which he controls and utilizes in the transportation of freight and 
commodities of aU kinds. The ants must necessarily have been intro- 
duced to this country by means of ships, and railways have been the 

• The "batture" is that land lying between the true bank of the river and the levee. The batture is 
subject to overflow during high water, is ordinarily not cultivated, and is frequently overgrown with wil- 
lows. The batture is said to be "outside" the levee, while land protected by the levee from high water is 
said to be "inside" the levee. 



MEANS OF DISPERSION. 21 

principal means of dissemination since they succeeded in establishing 
themselves. This is evident, as all the centers of infestation so far 
discovered, with the exception of those down the Mississippi River, 
the presence of which has just been explained, are located upon 
railway lines; in the Southern States, upon main lines running out 
of New Orleans. 

The ants are easily transported in packing and freight of various 
kinds. Large numbers of potted plants are shipped out of New 
Orleans to the surrounding country, and in many cases complete 
colonies of ants are sent with them in the soil surrounding the roots. 
Boxes and barrels of groceries, packing placed around fragile material 
to prevent breakage, and shipments of household goods may all 
contain queens and workers when shipped from infested points. The 
writer has observed a queen and many workers inside an empty 
passenger coach, which had been standing on the track for several 
hours during a rainstorm. 

The danger of promiscuous infestation is somewhat lessened by the 
fact that it is necessary for a queen ant to be transported with the workers 
in order that a new colony may be founded. In a large series of ex- 
periments conducted to determine this point we have never yet found 
any indication that the workers were able to produce eggs, or to 
reproduce their kind in any manner. Consequently large numbers 
of workers may be scattered broadcast over uninfested territory and,- 
though they may live for a considerable time, they will ultimately 
die out if a queen is not present. It is probably due to this fact that 
these ants have not infested a great deal more territory than they 
have during the past 10 years, as it is a certainty that thousands 
of workers are being continually shipped from infested territory into 
uninfested localities. At the same time the danger that fertile 
queens will be transported is considerable, for we have frequently 
found dealated queens foraging with the workers. The fertile queens 
will "take up " with any workers of the species, and it is only necessary 
for a queen and workers to be present iii a new locality in order to 
start a self-perpetuating infestation. 

Steamboats plying up and down rivers, carrying freight from 
infested points, are responsible for spreading great numbers of ants. 
For example, between New Orleans and Baton Rouge, La., there are 
over a hundred steamboat landings. These are nearly all infested 
by the Argentine ant, and probably the insects were first introduced 
in the freight shipped direct to these points from New Orleans or 
Baton Rouge. Many of the river steamboats are so heavily infested 
by permanent colonies of this ant that the workers are almost as much 
of a nuisance in the cook's galley as they are in culinary establishments 
on shore. 



22 THE ARGENTINE ANT. 

ECONOMIC IMPORTANCE. 

Up to the present time the Argentine ant lias attracted most atten- 
tion as a household pest. Particularly during rainy weather, when 
honeydew is scarce, the ants invade houses in myriads and drive the 
housekeepers almost to distraction. Nearly everything which is 
edible for human beings is attractive to them, and ceaseless attention 
and strenuous effort are necessary to keep them out of pantry and 
kitchen. The use of poisons and repellents must be continuous; 
if there has been a little carelessness in this regard the foodstuffs 
become filled with countless numbers of ants in a very short time. 

Among the foodstuffs most eagerly sought may be mentioned 
honey, sirups, sugar, candy, cakes, cookies, jams, marmalades, pre- 
serves, fruit juices, cream, olive oil, lard, egg (either raw or cooked), 
fish (either fresh or canned), and various raw meats, such as chicken, 
veal, mutton, pork, beef, etc. Corn meal is sometimes the object 
of attack and wheat flour to a slight extent. 

Aside from their invasions of food the ants are household nuisances 
generally. No corner or nook is safe from their explorations and the 
discovery of something edible is quickly heralded in the nest, whence 
come thousands of workers to carry away the plunder. In heavily 
infested sections it is often necessary to place bedposts upon panes of 
glass coated with vaseline or other repellent in order that the occu- 
pant may sleep in peace. To have ants running all over one's person 
is disagreeable enough, but what is more serious, they will not hesitate 
to attack any part of the body where skin or membranes are tender 
enough to be pierced by their mandibles. 

Authentic cases are on record where it has been necessary to take 
babes from their cradles and repeatedly immerse them in water to 
rid them of the ants which crawled by hundreds over their bodies 
and into their mouths and nostrils. We have even received reports 
of infants being killed by the ants, but such reports we have not 
verified. Such a thing is not, however,, outside the realm of 
possibility. 

In groceries and stores they are kept out of sirups, sugar, molasses, 
and like products only with great difficulty. In restaurants and 
confectionery shops the closest vigilance is required to keep the ants 
out of the cakes, candies, ice cream, fruits, etc., as well as out of ice 
boxes, refrigerators,^ show cases, and windows. Meat in butchers' 
shops is also a great attraction, and if left unprotected for even a 
short time thousands of ants will be swarming over it. 

In nurseries and among ornamental plants the ants foster and 
protect countless thousands of scale insects and plant lice, the excre- 
tions of which furnish the choicest delicacy with which the ants 

1 The temperature of the ordinary refrigerator is not low enough to deter the ants in theii- foraging. 



ECONOMIC IMPORTANCE. 23 

reo-ale themselves. This protective care results in rapid increase of 
these insects, with resultant damage to the plants infested. In 
florists' establishments the ants sometimes sever the petals of cut 
flowers in thek search for nectar. 

Visits to flowers of various kinds seem a natural habit, and when 
the ants do not find the nectar readily available they quickly cut 
theii' way to it m all cases where the plant tissue is tender enough 
to permit of it. In theii* attacks upon orange blossoms they are 
particularly severe, as they sometimes eat their way into the fruit 
buds even before the latter are fully open. The workers have also 
been noticed regularly visiting the extra-floral nectaries of cotton 
and other plants. 

To truck growers the ants are very troublesome, owing to the 
manner in which they remove certain garden seeds before they have 
sprouted. Lettuce seed is especially subject to this attack, and in 
infested districts the rows of lettuce seed are covered with corn meal, 
which is also attractive to the ants. By the time cho ants have 
removed the meal the lettuce seeds will have sprouted. The ants 
also assiduously attend plant lice on a number of vegetables, making 
the latter unpleasant to handle. Cabbage heads are often found 
through which plant lice and ants are completely distributed, the 
cabbage leaves merely serving as divisions between layers of the 
insects. 

In the sugar-cane fields the ant again comes to the front, owing 
to its fondness for the excretions of the sugar-cane mealy-bug, 
Pseudococcus calceolaride. (See figs. 3, 4.) In order to protect 
these insects from storms and enemies, the ants build protective 
coverings and shelters over them and attend them constantly. (See 
fig. 5.) As the result of these attentions the mealy-bugs thrive in 
numbers and destructiveness to an extent which is impossible where 
the ants are not present. Luckily the territoiy infested by the 
mealy-bug is as yet very restricted, but this insect threatens to 
become a serious problem in the future, owing to the manner in 
which it destroys the eyes of "seed cane" after it is planted, prevent- 
ing sprouting and thus injuring the stand. The vacant rows in a 
field of cane, due to this injury, are shown in figure 3. The control of 
this mealy-bug therefore resolves itself mto the problem of controlling 
the ant. 

In cornfields it can be easily noticed that aphides are several times 
as numerous, and are also more generally distributed, in districts 
infested by the Argentine ant than in the noninfested districts. The 
ants are also found in great numbers attending plant lice upon cotton 
plants, and in a cotton field at Baton Rouge, where these ants were 
veiy numerous, it was noticed that the cotton aphides remained 



24 



THE ARGENTINE ANT. 



abundant throughout the entire summer and autumn, whereas 
durmg these portions of the year they are normally almost absent. 
It is m the orange groves of southern Louisiana, however, that 
this ant has probably inflicted the most serious injuiy. This injuiy 
is discussed at length on a subsequent page. Suffice it to say that 
at present the Argentine ant is there regarded as the most serious 
insect problem, owing to the marked increase of scale msects which 
follows its introduction and spread. The value of land in that 
section depends to a considerable extent upon the presence or absence 
of the Argentine ant. The ant also does considerable damage to the 
fig crop by boring through the ripened fruit or entering the calyx end 
of the ripening fig and tunneling the interior. It also assists in the 




Fig. 3.— Injury to the stand of sugar cane by the sugar-cane mealy-bug Wscudococcuii calceolarlse), which 
is attended by the Argentine ant. (Original.) 

increase of the destructive mealy-bug, Pseudococcus citri, which 
injures figs to a considerable extent. 

The ant is a veritable plague among honey bees, and beekeeping 
on any considerable scale is invariably abandoned after the ants 
become numerous. 

In the poultiy yard this ant is a pest that must be reckoned with. 
The ants find the nests of sitting hens particularly attractive, and if 
perchance an egg be broken the ants will come in such numbers that 
the fowl will abandon her nest. The blood and fluids from partially 
incubated embryos are particularly liked by the ants, and when the 
eggs are hatching the workers swarm over the young chicles in such 



ECONOMIC IMPORTANCE. 



25 



numbers as to cause their death. Repellents which can be adapted 
to such a case are rare, even pyrethrum powder being practically 
ineffective. The only substance we have found which would at all 
protect the sitting hens is zenoleum powder, liberally sprinldod 
in the nest and among the hen's feathers from time to time 
during the brooding period. The nests of many bhds are 
frequented by the ants in the same way, and the number of 
young birds destroyed in this manner must be considerable. The 
ubiquitous English spar- 
row, however, seems to 
flourish, as ever, in spite 
of the ants. 

Another form of injury, 
though indnect, is due to 
the antagonism which ex- 
ists between the Argentine 
ant and other species of 
ants, and which terminates 
only with anniliUation of 
the native species. As the 
result of this, beneficial 
species of ants (such as the 
"fire unt," Solenopsisgemi- 
nata, which destroys a con- 
siderable number of boll 
weevils in their immature 
stages) are exterminated, 
and theu" place is taken by 
the infinitely more trouble- 
some Argentine ant. 

It may presently be 
found that the Argentine 
ant is an important agent 
in the spread of disease. 

The workers COncrecate Ul ^'*^- 4.— Sugar-cane mealy-bugs on sugar cane. (Original.) 

great numbers around garbage pails, privies, etc., and are frequently 
very hard to keep out of sick rooms, the odors seeming to attract them. 
They have been watched busily carrymg away the sputum of a negro 
who was suffering from tuberculosis. There are many ways in 
which it is possible for these ants to assist in the distribution of 
various disease-producing organisms. 

Rarely the activities of this ant take on a beneficial aspect. Father 
Biever states that they have in many cases completely exterminated 
the bedbugs in the hovels and tenements occupied by poor people in 
the city of New Orleans. The same authority several years ago 




26 



THE ARGENTINE ANT. 



called attention to the scarcity of the common "chiggers" or so-called 
"red bugs" in parks and yards heavily infested by the ant, and this 
latter observation has been verified by the junior author in the case 
of Audubon Park, New Orleans. At Baton Rouge, however, the 
senior author found the ''chiggers" very abundant in premises heav- 
ily infested by the ants. The manner in which these ants destroy 
the sorghum midge is described on following pages. 

SYSTEMATIC POSITION. 

According to the classification adopted by Dr. W. M. Wheeler/ 
the Argentine ant is placed in the subfamily Dolichoderinse, wliich 




Fig. 5.— Covering constructed by the Argentine ant to protect the mealy-bugs. (Original.) 

is one of the five main subdivisions of the family Formicidae. The 
Dolichoderinas are characterized by the cloacal orifice being slit- 
shaped and ventrally located instead of being circular and termi- 
nally located, as in the camponotine ants, by vestigial sting, by 
single-segmented abdominal pedicel, by a much shortened or bell- 
shaped gizzard (proventriculus), by the pupae being always naked 
(not inclosed in cocoons), and usually by anal glands which produce 
a secretion having a very offensive odor. In the case of the Argen- 
tine ant, however, this odor is entirely lacking. 

1 "Ants, their structure, development, and behavior," 1910. 



SYSTEMATIC POSITION. 27 

The subfamily Dolichoderiiise contains six North American genera : 
Dolichoderiis (Hypoclinea), Forelius, Tapinoma, Dorymyrmex, Lio- 
metopum, and Iridomyrmex. Iridomyrmex is essentially tropical in 
its distribution and only two species are known to occur in the United 
States/ the native Iridomyrmex analis Ern. Andre, common in cotton 
fields of the South, and the introduced species, Iridomyrmex Tiumilis 
Mayr, or Argentine ant. 

DESCRIPTION OF THE SPECIES. 

Three forms only of the adults are found in the colonies of the 
Argentine ant, the females or queens, the workers, and the males. 
(See fig. 6.) Major and minor w^orkers do not occur, and no workers 
seem to act in the capacity of soldiers or scouts more than others. 
As previously noted, the species was first described as Hypoclinea 
humilis by Dr. G. Mayr, in 1868, from workers collected in 1866 near 
Buenos Aires in Argentina, the original description appearing in the 
Amiuario deUa Societa dei Naturalisti di Modena, volume 3, page 
164. Following is Mayr's description of the species kindly fur- 
nished by Dr. W. M. Wheeler, of the Bussey Institution, Harvard 
University, from the original edition: 

Operia: Long. 2.6 mm. Sordide ferruginea, micans, mandibularum parte apicali 
flavescenti, abdomine nigrofusco, tarsis et nonnunquam tibiis testaceis; microscopice 
adpresse pubescens; absque pilis abstantibus; subtilissime coriaceo-rugulosa, mandi- 
bulis nitidis sublaevigatis punctis nonnullis; clypeus margine antico late haud pro- 
funde emarginatus; thorax inter mesonotom et metanotum paulo et distincte con- 
strictus, pronoto fornicato, mesonoto longitrorsum recto, transversim convexo, meta- 
noto inermi longitrorsum fornicato, pronoto paulo altiori; petioli squama compressa 
rotundata. 

At the request of the senior author. Dr. Wheeler prepared the fol- 
lowmg redescription of the worker, and descriptions of the queen 
and male, thus making a complete and comprehensive description 
of the species: 

Iridomyrmex humilis Mayr. 

Worker: Length 2.2-2.6 mm. 

Head oval, broader behind than in front, with its posterior margin slightly concave 
in the middle. Eyes flattened, in front of the middle of the head. Mandibles with 
two larger apical and several minute basal teeth. Clypeus short, convex in the mid- 
dle, with broadly excised anterior margin. Frontal area and groove present but 
rather indistinct. Antennal scapes extending about one-fourth their length beyond 
the posterior comers of the head. Joints 1-5 and the terminal joint of the funiculus 
distinctly longer than broad; remaining joints nearly as broad as long. Thorax slen- 
der, narrower than the head; broadest tlirough the pronotum which is convex, rounded 
and nearly as long as broad. Mesonotum nearly as long as the pronotum, sloping, 
laterally compressed, in profile evenly continuing the contour of the pronotum. Me- 

' An undetermined species of Iridomyrmex, apparently introduced, has been found by Dr. W. M. Wheeler 
In a greenhouse at Boston, Mass. 



28 



THE ARGENTINE ANT. 



soepiiiotal constriction rather deep, extending obliquely downward and backward on 
each side. Epinotum short, nearly twice as high as long, convex on the sides, with 
a short convex base, and a longer, flatter and more sloping declivity. Petiole small, 
less than half as broad as the epinotum; its scale in profile, compressed, cuneate, 
inclined forward, with flattened anterior and posterior surfaces and rather acute apex; 
seen from behind its border is entire and evenly rounded or even slightly produced 
upward in the middle. Gaster small. Legs rather slender. 




Fio. G. — The Argentine ant, adult forms: a, Adult male; at, head of male; a2, petiole of male; h, worker; 
hi, head of worker; hi, petiole of worker; c, fertile queen; cl, head of queen: c2, petiole of queen. All 
greatly enlarged. (Senior author's illustration.) 

Body minutely shagreened or coriaceous, subopaque and glossy; mandibles, clypeus 
and anterior border of the head more shining. Mandibles minutely and rather ob- 
scurely punctate. 

Hairs few, suberect, yellowish, confined to the mandibles, clypeus, tip and lower 
surface of the gaster. Pubescence short and uniform, grayish, so that the body has a 
slightly pruinose appearance. 



SYSTEMATIC POSITION. 29 

Brown; thorax, scapes and legs somewhat paler; mandibles yellowish; apices of 
the individual funicular jomts blackish. 

Female (dealated): Length 4.5-5 mm. 

Head, without the mandibles, but little longer than broad, with rather angular pos- 
terior corners, straight, subparallel sides and straight j^osterior border. Eyes large and 
rather convex. Mandibles and clypeus like that of the worker, scapes proportionally 
shorter and stouter. Thorax large, as broad as the head, elongate elliptical, nearly 
three times as long as broad. In profile the scutellum is very convex, projecting 
above the meso- and epinotum. Epinotum with very short base and long abrupt 
declivity. Petiolar node erect, more than half as broad as the epinotum. Gaster 
elliptical, somewhat shorter and a little broader than the thorax. Legs slender. 

Sculpture like that of the worker but more opaque; mandibles and clypeus also 
less shining. 

Scattered hairs more numerous than in the worker and also present in small numbers 
on the vertex, gula, mesonotum, presternum, and fore coxae. There is also a row of 
short hairs along the posterior margin of each gastric segment. Pubescence dis- 
tinctly longer, more silky, and denser than in the worker. 

Dark brown; antennae, legs and posterior margins of the gastric segments reddish; 
mandibles, sutures of thorax and articulations of legs yellow. 

Male: Length 2.8-3 mm. 

Head much flattened; including the flattened eyes, as broad as long. Vertex and 
ocelli prominent. Cheeks short. Mandibles small, overlapping, with a single, acu- 
minate apical tooth. Anterior clypeal border straight. Antennae slender; scape 
only between three and four times as long as broad; first funicular joint globose, 
broader than any of the other joints; second joint much longer than the ;cape; joints 
3-5 growing successively shorter; joints 6-12 considerably shorter and more slender. 
Thorax very robust, elliptical, broader than the head, which is over-arched by the 
protruding, rounded mesonotum. Scutellum even more prominent than in the female. 
Epinotum with subequal base and declivity, the former slightly convex, the latter 
feebly concave, forming an angle with each other. Petiole small, its node with rather 
blunt margin, slightly inclined forward. Gaster very small, elongate elliptical, with 
small rounded external genital valves. Legs slender. Wings with a four-sided discal 
cell and two well develojied cubital cells. The costal margin is depressed or folded 
in just proximally to the stigma. 

Sculpture, pilosity and pubescence as in the worker; color more like that of the 
female, except that the antennae, legs, mandibles and internal genitalia are pale, 
sordid yellow. Wings smoky hyaline, with brown veins and stigma. 

/. humilis belongs to a small group of neotropical species embracing also I. iniquus 
Mayr, dispertitus Forel, keiteli Forel and melleus Wheeler. The workers of keiteli and 
melleus may be at once distinguished by their color, the former having a yellowish 
brown head and thorax and the remaining parts brownish yellow; the latter being 
pale yellow with a blackish gaster and funiculus. In these and in /. iniquus and 
dispertitus the mesoepinotal constriction is much deeper than in humilis and the meso- 
and epinotum are of a different shape. The mesonotum in profile does not form a 
continuous, even line with the pronotum and the epinotum is very protuberant and 
almost conical. J. humilis represents a transition from the above group of species 
to that of /. analis Ern. Andre, which is very common in the Southern States. This 
species has a shorter, more robust thorax, more like that of Tapinoma, and much less 
constricted in the mesoepinotal region. 

The above description was drawn from a number of workers, males and females 
taken from the same nest in Baton Rouge, La., by Mr. Wilmon Newell. The types 
described by Mayr were captured by Prof. P. de Strobel in the environs of Buenos 
('ires. 



30 THE AEGENTINE ANT. 

RESEMBLANCE TO OTHER ANTS. 

There is little difRculty in distinguishing Iridomyrmex humilis 
Mayr from its nearest American relative, Iridomyrmex analis Ern. 
Andre. The latter species is quite common in cotton fields and other 
situations in the South, is much lighter in color than humilis, and 
possesses a very disagreeable odor which is entirely lacking in the 
case of humilis. The clearly marked trails of the Argentine workers, 
when on their foraging expeditions or when moving from place to 
place, have no counterpart in the case of analis, the workers of which 
in large measure forage independently of each other. I. analis 
constructs inverted cone-shaped mounds or craters on the surface 
above the underground nests, while what little dirt is excavated by 
humilis is scattered about the entrance to the nest in promiscuous 
fashion, the ants evidently desiring to rid themselves of the exca- 
vated pellets as expeditiously and conveniently as possible. The 
''wet-weather sheds" of the Argentine ant, constructed only during 
or just after prolonged rainy spells, bear no resemblance whatever 
to the craters of analis; but on the contrary are more or less flat, 
composed of fine particles of earth, unstable in structure and supported 
by grass or leaves. 

However, the superficial resemblance of 7. humilis to several spe- 
cies of other genera is even closer than to /. analis and is sufficient 
to make positive identification of humilis well-nigh impossible ex- 
cept by one skilled in detecting the characters used by myrmecolo- 
gists for classification. Among the southern forms most likely to 
be mistaken for /. humilis, and vice versa, may be mentioned the 
"crazy ant" (Prenolepis longicornis Fab.) and Dorymyrmex pyra- 
micus Roger. The workers of both these species are of practically 
the same size and color as those of humilis and the workers of all three 
travel and forage in much the same way. Prenolepis is distinguished 
from 7. humilis by its camponotine characters, particularly the shape 
of the gizzard, by the cloacal orifice being round rather than slit- 
shaped, and by the presence of stifi^, erect hairs upon the body. Dory- 
myrmex is easily distinguished by the conical or pointed elevation 
upon the epinotum (last dorsal segment of the thorax), a structure 
that is entirely lacking in Iridomyrmex, the epinotum of which is 
evenly convex. 

The resemblance of 7. humilis to still other species is sufficient to 
be confusing at times, but one can, by a process of ehminating certain 
'easily observed characteristics, determine mth reasonable probabihty 
whether a colony of Hving ants belongs to this species or not. First 
to be noticed is the size of the ants under suspicion. The workers of 
the Argentine ant are from 2.2 to 2.6 mm. in length, the largest indi- 



SYSTEMATIC POSITION. 31 

vidual we have ever seen measuring 2.75 mm. If workers are more 
than 3 mm. or less than 2 mm, in length, it may be safely concluded 
that the ant under observation is of some other species. The Argen- 
tine queen, however, is from 4.5 to 5 mm. in length. The color of 
the Argentine ants— all adult forms — is a very deep brown, ahnost 
approaching black, and the color is uniform over the entire body. 
The possession of head and thorax of one color with abdomen of a 
different color immediately eliminates a specimen from this species. 
A colony containing workers of more than one size is also eUminated, 
since all Argentine workers are of one size or caste. The fact that the 
petiole or pedicel (connecting joint between the thorax and abdomen) 
of /. Tiumilis consists of only one segment readily distinguishes it from 
the species of Solenopsis and other myrmicine ants. The pupae of 
our species is never inclosed in cocoons, but always naked, with legs, 
eyes, segments, etc., plainly visible. Argentine workers, when 
crushed between the fingers, give no perceptible odor, and this readily 
distinguishes them from their closest relative, /. analis, as well as 
from their more remote relatives, the species of Tapinoma. The 
Argentine worker does not possess a functional sting and does not 
even attempt to sting. This again separates the workers from those 
of a great many species, including Solenopsis, most of which sting 
viciously upon the slightest provocation. Upon being disturbed, 
particularly in the nest, some of the Argentine workers will attempt 
to bite, but by far the great majority devote their energies to escaping 
rapidly or to removing the larvte and pupje to a place of safety. 
What few do attempt to bite are not successful in piercing the skin 
of one's hands owing to their weak jaws. It is only when reaching 
tender places, such as the skin between the bases of the fingers for 
example, that they are able to make their bites effective. 

If, therefore, ants suspected of being Iridomyrmex Tiumilis meet the 
following quahfications, and in addition exhibit the habits already 
described, there is a reasonable probability that they belong to this 
species, and examples should be submitted to a specialist for exam- 
ination: 

Workers not over 3 mm. nor less than 2 mm. in length 

Workers uniformly colored; deep brown, nearly black. 

Workers of uniform size; no distinction as to caste. 

Workers traveling in well-defined trails or lines to and from the nest. 

Workers emitting no offensive odor when crushed. 

Workers unable to sting and unable to bite effectively. 

Pupsp not inclosed in cocoons. 

Petiole or pedicel consisting of only one segment. 

Petiole prolonged dorsally into a wedge-shaped scale, inclined slightly forward. 

Epinotum devoid of a pointed or conical elevation. 

Ocelli absent in workers, present in queens and males. 



32 THE ARGENTINE ANT. 

METHODS OF STUDY. 

When the study of this ant was undertaken, two requisites presented 
themselves — a type of artificial formicary in which continuous obser- 
vations could be made and individuals kept track of from the time of 
egg deposition until the adult stage was reached, and some method 
by which all individuals of a colony could be confined to their own 
formicary. 

Space need not be taken to describe the types of artificial formicaries 
which were not successful. 

The Janet cages proved successful only in the case of very large 
colonies, but in these the multiphcity of individuals made accurate 
observations impossible. It may be remarked that this type of cage 
is excellent for stud3dng the community life as a whole and for making 
experunents with poisons or with parasitic fungi or bacteria. 

Cages totally inclosed were not successful, for the reason that the 
ants, when deprived of the privilege of leaving their nest, failed to act 
in a normal manner. 

The cage finally adopted was, with modifications, the one described 
by Sir John Lubbock on pages 2 and 3 of his classic work.^ This 
consists essentially of two glass plates containing between them a 
layer of pulverized earth in which the ants may burrow at their 
pleasure. Considerable difficulty was experienced in getting the 
glass plates the proper distance apart; if too far apart the ants could 
make burrows which were not open to observation, and if too close 
together insufficient room was afforded the queen in which to stand 
and walk upright. As the queen is about twice as tall as the worker, 
it seemed for a time that a suitable cage could not be constructed. 
After repeated trials, however, it was found that if the space between 
the glass plates were made exactly 1.75 mm. the queen would have 
sufficient room and the workers could not construct invisible galleries. 

This type of cage and its supporting stand are well illustrated by 
figures 7 and 8. Figure 7 shows the several parts of the cage; 3 is the 
cage proper, consisting of two plates of glass held uniformly 1.75 
millimeters apart by strips of leather at all four edges, a door or open- 
ing being left at one corner. (See fig. 9.) Old negatives, the films 
removed with caustic soda, have been found the most desirable for 
making these cages, both because such glass is remarkably clear and 
free from imperfections and because it is of uniform thickness. The 
size of the cage may vary from 3^ by 41 up to 8 by 10 inches or even 
larger. Leather was found more satisfactory for making the edges 
of the cage than either glass or wood. The strip of leather between 
the glass margins is about | inch in width. It is extremely difficult 
to find a strip of glass uniformly 1.75 millimeters thick and it is also 

1 Avebury. Ants, bees, and wasps, 1881. 



Bui. 122, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate II. 




A Small Colony of Argentine Ants as Seen in one of the Artificial Formicaries. 

(Original.) 



METHODS OF STUDY. 



33 



difficult to attach one piece of glass to another firmly. Wooden 
strips present the disadvantage of quickly decaying and of warping, 
no matter what glue or cement is used to hold them in position. Since 
it is sometimes desirable to place moist earth in the cages, or to add 
moisture from time to time, a waterproof cement is most desirable 
for attaching the glass plates to the leather strip. The s]5ace between 
the glass plates is filled with finely pulverized earth after completion 
and drying of the cage, and in this the ants are permitted to burrow 
and construct galleries as they please. (See PI. II.) 

The cage proper is supported on a platform (1) which in turn rests 
firmly upon a standard (2) having a base (4)- The platform must 
have its upper surface perfectly level and it must remain so for an 




Fig. ".—Artificial formicary or cage used in studying the Argentine ant: /, Supporting platform; S, stand- 
ard; 3, cage proper, made of glass and leather, containing earth; 4, base; S, cover. (Senior author's 
aiustration.) 

indefinite time, otherwise the ants will take up their abode between 
the cage and platform rather than in the cage itself. The platform is 
therefore made of two pieces of even, seasoned cypress | inch thick, 
screwed together with numerous screws and with the grain of the 
two pieces at right angles to each other. On this platform the cage 
rests without fastenings of any kind. The cover (5) is constructed of 
two pieces of cypress in the same manner as the platform, but in 
addition has an iron handle attached to its upper surface and has a 
piece of felt glued to its under surface, so that, when it is placed upon 
the cage proper, all light is excluded except at the entrance. The 
cover is of the same outside dimensions as the cage itself. To insure 
the platform remaining level it is often necessary to make the base 

75508°— Bull. 122—13 3 



34 



THE ARGENTINE ANT. 



of two pieces in the same manner as the platform, or to nail strips 
across it at right angles to the grain. Both platform and base are 
attached to the standard by long screws with heads countersunk. 
Food is furnished by placing it on a piece of cardboard at any point 
on the cover or platform. The base stands in running water, as 
explained below. This type of cage permits the ants to leave their 
nest within the cage and to forage over the platform, cover, and stand 
in natural fashion, but their escape from the stand is prevented by the 
very natural barrier of water, which they find when they approach the 
bottom of the standard. It is not possible for them to conceal larvse 
or eggs where the observer can not find them and they can not bring 




Fig. 8.— .Vrtiflcial formicary with parts assembled ready for use. (Senior author's illustration.) 

in larvae or pupge from outside sources to the annoyance and vexation 
of the student. 

While the ants are very fond of sweets, we have found that sweets 
alone will not suffice for food indefinitely. Animal food is also 
required, and we find that by supplying the colonies with a "balanced 
ration" of honey and fresh beef or veal they will work in a perfectly 
natural manner for many months without other food. 

The problem of confining the ants to the cage and its stand was not 
so easily solved. We first tried Sir John Lubbock's method of plac- 
ing a moat of glycerine or water about the stand, but both liquids 



METHODS OF STUDY. 



35 



dried too quickly and were effective for only a few hours. Recourse 
was had to the proverbial chalk hne without success. Bands or 
ditches of kerosene, crude oil, tar, oils of sassafras and citronella, tree 
tanglefoot, zenoleum, naphthaline, coal-tar disinfectants, whale-oil 
soap, sharp-edged tin, and fur were all failures. Certain powerful 
odors, such as those of zenoleum, sassafras, and citronella, act as 
repellents temporarily, but after a few hours of evaporation are no 
longer effective. Ordinarily these ants will not cross bands of cotton 
tape which have been impregnated with a saturated solution of cor- 
rosive sublimate and dried, but when attempting to leave an area to 
which they have been confined by this means they are much more 
persistent in crossing it. 

Water with a film of whale-oil soap on it acted as a repellent for a 
few hours only, while a film of kerosene upon water merely afforded 




Fig. 9. — Entrance of artificial formicary shown in figures 7 and 8. (Senior author's illustration.) 

a convenient floor upon which the ants could travel. The difficulty 
in confining the workers with any liquid or mucilaginous substance 
lies in the fact that they are exceedingly light,* and sticky substances 
shortly harden on the surface, so that the workers are supported. 
The surface film of clear water is in fact almost strong enough to sup- 
port a worker not loaded. It is not unusual to see an ant alternately 
walking and swimming in crossing a narrow ditch of water which has 
been standing for a few hours. Minute dust particles collecting upon 
standing water shortly form a film upon which the workers pass with 
ease. Perfectly fresh water therefore served to confine the colonies 
to their cages, and at first our observations were made upon colonies 
in cages which were standing in dishes of water. This, however, 
necessitated frequent changing of the water, and observations were 
often brought to an abrupt finish by other duties which prevented 
the change of water in the vessels at the right time. 

1 The average weight of one worker is 0.0002077 gram. 



36 THE AKGENTINE ANT. 

In February, 1908, the senior author constructed, on the grounds 
of the Louisiana Experiment Station at Baton Rouge, a small build- 
ing for the purpose of studying this ant more in detail. The building 
was 10 by 30 feet and equipped with benches having upon them gal- 
vanized iron trays 2^ by 12 feet, 4 inches deep. In these trays the 
cages were placed and by means of suitable connections running 
water 2 inches in depth was kept passing through the trays day and 
night. As the ants would not voluntarily enter running water this 
arrangement worked admirably. The interior arrangement of this 
building is shown in Plate III. The iron trays and ant cages are 
shown upon the right, with work tables, chemicals, etc., on the left. 
The building was ec{uipped with electric and extension lights for 
night examinations, and a combined thermograph and hygrograph 
recorded the temperature and humidity of the room at all times. 
For convenience this building was referred to as the ''formicarium." 
Plenty of windows insured full ventilation at all seasons, and to avoid 
abnormally high temperature in summer a second or accessory roof 
was placed two feet above the main roof. This laboratory also 
proved a convenient insectary for the rearing of other insects. 

The Argentine ant possesses a marked proclivity for attacking aU 
insects which one has under observation, and all rearing experunents in 
cages, no matter what the insect, must be protected from the ants. 
The trays of running water therefore served to keep the ants away 
from general cage experiments as well as to confine them to the cages 
in which they themselves were bemg studied. 

ESTABLISHING COLONIES FOR STUDY. 

To establish a colony in one of the artificial formicaries or cages is 
comparatively easy. It is only necessary to secure a fertile queen 
from some thriving outdoor colony and place her on the stand, first 
placed in water, together with any desired number of workers which 
have been captured by attracting them to a sweetened sponge or 
piece of fresh meat. Any lot of workers will accept any queen and 
vice versa. When queen and workers are thus placed upon the cage 
and its stand, they usually, after a few hours, take up their abode 
in the nest proper. At first we experienced some difficulty in pre- 
venting them from collecting beneath the stand, but it was presently 
found that if a little dirt were removed from another colony and placed 
in the entrance of the new formicary the ants would enter at once and 
adopt it as a suitable home. After the establishment of such colonies 
the queen usually commences o^gg deposition in from 6 to 48 hours. 

By establishing colonies in this manner, witnout immature stages 
present, it is easy to observe the daily rate of egg deposition, the 
incubation period of the eggs, and the duration of the larval and pupal 



Bui. 122, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate III. 




METHODS OF STUDY. 37 

stages. In some of the records given below single individuals have 
been kept under observation from deposition of the egg, through larval 
and pupal stages, to the adult. In other cases the time from deposi- 
tion of the first egg until hatching of the first larva was assumed to be 
the period of incubation, date of hatching of first larva to formation 
of first pupa the duration of the larval period, etc. 

While these cages were invaluable in studying the life history of the 
ants, the small amount of space available for them between the glass 
plates made the number of ants they would contain very limited. For 
the purpose of studying the general habits of large colonies of ants a 
modification of the Janet cage was used. As its name implies, this cage 
was invented by Mr. Charles Janet, ^ and is described by him as follows: 

The apparatus (an artificial horizontal nest of porous mineral substance) described 
in this treatise gives, in reference to the raising of ants, remarkable results. Ants die 
in a short time when placed where they can not receive sufficient nioisture; but (and 
this is the delicate pomt) this moisture must be maintained within certain limits. 
The apparatus invented up to the present do not solve this difficulty. Furthermore, 
they do not lend themselves easily to observation, nor do they permit one to withdraw 
with ease specimens when needed. The artificial nest is formed of a block of plaster, 
or any other porous substance, which has hollowed out of it a certain number of small 
cells, placed one after the other and communicating. These cells are covered with an 
opaque slab designed to keep the cells dark between the periods of observation. A cup 
of water placed at the end of the block allows it to absorb moisture. The cell nearest 
this cup is the dampest, and the one farthest away the driest. I leave this last always 
light so that it resembles, for the breediug under observation, a space outside of the 
nest. If the water-cell has been kept too moist, the ants go into the cell farthest away, 
that is to say the driest. When, on the contrary, the apparatus becomes too dry the 
ants return to the walls of the cell containing the water, which is always damper than 
the other parts of the nest. They can thus choose for themselves the part of the nest 
presenting the degree of moisture which suits them best. 

The chief modification adopted was the use of a five-celled cage 
instead of one of four cells, as described by Janet. Also, the ants 
were not inclosed within the cage, but were allowed to enter or leave 
at will. To permit of this the Janet cages were placed upon plat^ 
forms, which stood m running water. These platforms were consid- 
erably larger than the cages, and this gave the workers quite an area 
to forage over, simulating natural conditions quite closely. The food 
was placed upon the platform, outside the nest, and the workers thus 
had to carry it m and feed the larvae in the same manner in which it 
was done outdoors. These cages had sufficient capacity for many 
thousands of ants. They were used for observing the behavior of 
large colonies and for the purpose of noting the effects of poisons 
and various control measures. 

1 studies on ants. Note 2. Apparatus for the raising and observation of ants and other small animals 
which require a moist atmosphere. Extract Ann. Ent. See. France, Mar. 10, 1893; vol. 62, pp. 467-482, 
figs. 11-12. (Translated by Miss A. O'Conor.) 



38 THE ARGENTINE ANT. 

LIFE HISTORYo 
THE EGG. 

(PI. IV, A.) 

The egg is elliptical, pearly white, lustrous, without markings, and 
the membrane is extremely tliin and delicate. The surface is some- 
what mucUaginous, so that when eggs come in contact they adhere 
to each other. This enables the workers to handle them en masse and 
also permits of their being deposited upon the walls or ceilings of the 
ants' habitations. 

The average size is 0.3 mm. long by 0.2 mm. wide. The largest egg 
encountered while measuring a series was 0.34 mm. long by 0.24 mm. 
wide, and the smallest 0.27 ram. by 0.187 mm. 

As time for hatching approaches the luster fades and the surface 
takes on a dull appearance. This is not sufficiently pronounced and 
uniform, however, to be taken as a safe guide to immediate hatching, 
Wlien the embryo takes on the larval shape the membrane not infre- 
quently adapts itself in a way to the general contour of the inclosed 
embryo, thus making it very difficult to distinguish between the eggs 
and the newly-hatched larvae. 

In the large Janet style cages the workers seem to take elaborate care 
of the eggs in order to secure for them just the requisite amount of 
humidity. Frequently they will be shifted several times in the course 
of the day, first bemg stored in one corner, then moved to the center 
of the compartment, afterwards carried to another compartment, and 
perhaps finally stuck to the glass ceiling. Sometimes the eggs are 
separated from the larvae and pupae; at other times they will be stored 
together in apparently hopeless confusion. 

The care of the eggs by tne workers seems essential to complete 
embryonic development. Eggs deposited in test tubes by isolated 
queens have gone tlixough a portion of the embryonic development, 
but we have not been successful in getting them to hatch. Tliis may 
be due in part to the ease with which the delicate embryos are injured 
in handling and to the fact that when placed on glass the condensing 
moisture may retard or stop development. 

The queen appears to act merely as an egg-producing machine, and 
once the egg has been deposited she pays no further attention to it. 
The act of oviposition has been observed several times and does not 
occupy more than a few seconds of time. An attendant ant appears 
to be anxiously watching for the appearance of the egg, and it is 
immediately picked up and rushed off to the nearest "egg pile," 
sometimes before it has time to touch the floor of the nest. 

Attempts to get fertilized queens, unattended by workers, to 
deposit eggs and rear the resulting larvae to maturity have been 
unsuccessful. Such queens stop laying a few days after their isola- 
tion and seemingly pay no attention to what few eggs they do deposit. 



LIFE HISTORY. 



39 



Eggs are deposited at all seasons of the year. The large majority 
of them are produced during the summer, but a few are laid in warm 
spells during the winter months. The rate of deposition has not been 
determined, but one queen under observation in a cage deposited 
at the rate of 30 eggs per day, now and then suspending oviposition 
for several days at a time. 

In outdoor colonies oviposition ceases when the daily mean tem- 
perature drops below 65° F., but is usually begun again when the 
mean temperature rises above tliis point, regardless of the time of the 
year. 

No indication has been found of workers dep'ositing eggs, even in 
colonies that were queenless for long periods; neither did queenless 
colonies ever rear queens from the eggs and larvae present in the nest 
at the time queenlessness occurred. 

PERIOD OP INCUBATION. 

The period of incubation varies with the season of the year, and 
in proportion as the temperature remains high or low. The shortest 
incubation period observed has been 12 days, the longest 55 days, 
and the average is about 28 days. The longer periods are doubtless 
accounted for by the entire suspension of embryonic development 
during cool weather, and it is not impossible that the viability of 
eggs may be entirely destroyed by a temperature as low as 25° or 
30° F., but on this point more data are needed. 

The period of incubation has been determined, ordinarily, by 
placing a queen and workers, but no immature stages, in an artificial 
formicary and then noting the time from deposition of the first egg 
to appearance of the first larva. This period was assumed to be the 
real period required for incubation. In other cases single groups of 
eggs have been kept under constant observation tlu"oughout the 
entire period of incubation. The following table shows the variation 
in development at different seasons, together with the av^erage daily 
mean temperatures prevailing: 

Table II. — Duration of the egg stage of the Argentine ant at different seasons — worker. 



Record No. 


From— 


To— 


Days.' 


Average 
daily 
mean 
tempera- 
ture 
during 
pe'-iod. 


Average 
daily 
mean 

humid- 
ity. 


1 


Oct. 1,1907 
Dec. 22,1907 
Mar. 14,1908 
May 1,1908 
July 20,1908 
July 25,1908 
June 30, 1908 
July 24,1909 


Nov. 15,1907 
Feb. 14,1908 
Apr. 9, 1908 
May 23,1908 
Aug. 10,1908 
Aug. 12,1908 
July 18,1908 
Aug. 5, 1909 


45i 

55 

27 

23 

22 

19 

19 

12 


°F. 

(=) 
70.3 
74 

81 
81 

81.1 
82.5 


Per cent. 


3 




4 


70 2 


6 


68 9 


7 


82.9 


8 


81 5 


12 


74.9 


14 


78.8 







1 Average days, 27.8. 

2 Cages kept in office; record of exact temperatures not available. The balance of the records were made 
in the " forraicarium " and the recording instruments kept in the same room with the cages; hence the 
temperature and humidity records are correct for the exact location of the eggs under observation. 



40 THE ARGENTINE ANT. 

THE LARVA, 
(PL IV, B, C.) 

The larva when first hatched is not distinguishable from the egg 
without the assistance of a magnifying glass. For a time after 
hatching the body is considerably curved, the cephalic end being 
almost in touch with the caudal end, but as development progresses 
the larva assumes more and more of a straight form. The curvature 
is not entirely lost, however. 

A recently hatched larva, measured with the compound microscope 
and eyepiece micrometer, was 0.49 mm. long by 0.32 wide. The fully 
grown larvae (workers) average 1.7 mm. long by 0.66 mm. wide. The 
largest one under our observation measured 1.87 mm. by 0.765 mm. 

With the exception of slight constrictions of the body, the larvae 
are incapable of motion, thus being entirely helpless and relying 
altogether upon the ministrations of the attendant wori<:ers. The 
latter, however, perform their duties faithfuhy, and care for their 
charges with the greatest solicitude. They feed and groom the 
young larvae continually and transjiort them from place to place 
whenever necessary. In case of danger their fii'st instinct appears to 
be to remove the young to a place of safety, and they readily sacrifice 
their own lives in order to accomplish this. 

The larvae are fed often by the attending workers upon regurgitated 
and presumably predigested food. There is nothing in the appear- 
ance or actions of the workers which do the feeding to indicate that 
they are different from those which perform other duties, or that 
the}^ are assigned to the jmrticular and exclusive duty of being nurses. 
The feeding of the larvae has several times been observed under a 
magnifying glass, and is as follows: The larva ordinarily lies upon 
its side or back. The attending worker approaches from any con- 
venient direction, usually from one side or from the direction in which 
the head of the larva lies, and, spreading her mandibles, places them 
over the moutl^ parts of the larva, which are slightly extruded. The 
tongue of the worker is also in contact with the larval mouth. Wliile 
the worker holds the Body and mandibles stationary a drop of light- 
colored, almost transparent fluid appears upon her tongue. This 
fluid disappears within the mouth of the larva, but it can not be ascer- 
tained to what extent the larval mouth parts are moved during the 
operation, as they are obscured from view by the mandibles and head 
of the attending worker. Slight constrictions of the larval abdomen 
during feeding are sometimes noticeable, at other times not. The 
time required for feeding a single larva varies from 3 to 30 seconds, 
depending doubtless on the hunger of the *'baby." The workers 



Bui. 122, Bureau of Entomology, U. S. Dept. of Agriculture. 






Plate IV. 







Immature Stages of the Argentine Ant. (Original.) 

A, eggs; B, laivif and worker pnvKie; C, larva', more enlarged: D, piip;e of workers: at center, 
male pupa. All enlarged. (Senior author's illustration.) 



LIFE HISTORY. 41 

proffer food to, or at least inspect, each larva, for the worker doing 
the feeding will place her mandibles to the mouth of one larva after 
another, feeding those which seem to require it. 

Both larvae and pupsB are groomed or licked with the tongues of the 
workers; thus they are ever kept m a state of absolute cleanlmess. 

The most pronounced increase m size of the larvae occurs during the 
first five days after hatching. As is the case with other ants, nothmg 
is voided from the alimentary canal during the larval period, the 
undigested portions of the food being retained in the stomach, the 
latter having no open connection with the intestine. As the larva 
reaches its full growth this meconium, or mass of undigested material, 
becomes quite large and is distinctly visible as a dark object in the 
posterior portion of the body. At about this time, communication is 
established between stomach and intestine and the meconium is 
voided. The larva then enters the prepupal or semipupal stage. 
While the msect m this stage is not very different in appearance from 
a full-grown larva, close examination shows a number of slight differ- 
ences. Aside from the absence of the meconium, the cephalic and 
thoracic regions become markedly smooth and shining, w^th segmen- 
tation very indistinct, while the segmentation in the abdominal 
region is, if anything, more pronounced than before. The line of 
demarkation between abdomen and thorax is now in evidence, but 
without any very noticeable constriction. The mouth parts are 
protruded more than in the larva. The difference in appearance 
between larval and prepupal stages is not great but is sufficient to 
enable one to predict, with reasonable accuracy, the approaching 
transformation to the pupal stage proper. 

In the later portion of the larval stage we have first been able to 
distinguish between the males and workers. The male larvae grow 
to a somewhat larger size than do the worker larvae, and it is thus 
possible to predict with some degree of certainty wliich of grown 
larvae will transform to males and which to workers. In all other 
respects, however, they are apparently alike. The larval stage of the 
queen is unknown to us. 

DURATION OF THE LARVAL STAGE. 

The duration of the larval period has been determined by observa- 
tion in the artificial nests in the same manner as the incubation period 
already described. 

The following table shows, the duration of the larval period at dif- 
ferent seasons. 



42 



THE ARGENTINE ANT. 



Table III. — Duration of larval stage of the Argentine ant at different seasons — 

worker. 











Average 












daily 


Average 










mean 


daily 


Record No. 
1 


From— 


To— 


Days.i 


tempera^ 

ture 
during 
period. 


mean 
humid- 
ity. 










° F. 


Per cent. 


1 


Nov. 16,1907 
Feb. 5, 1908 


Jan 15,1908 


61 


52 2 




6 


Apr. 1,1908 
do 


57 


62.2 


71 9 


8 


do 


57 
43 


62.2 

62 


71.9 


10 


Feb. 15,1908 


Mar. 28,1908 


72 


3 


Feb. 29,1908 


Mar 20,1908 


27 


• 67 


73 


9 


Apr. 10,1908 
Apr. 12,1908 
July 19,1908 


Apr. 24,1908 
Apr. 25,1908 
Aug. 1,1908 


15 


76.6 


75.3 


7 


14 


76.1 


75.2 


2 


14 


80.5 


82 


11 


Aug. 13,1908 


Aug. 27,1908 


15 


81.7 


71.7 


4 


Sept. 4,1908 


Sept. 14,1908 


11 


81.1 


73.0 







1 Average days, 31.4. 



THE PUPA. 



When the pupal stage is reached by the young ant all doubt is 
removed as to the sex of the individual, for one can tell at a glance 
which pupae will transform into adult workers, which to males, and 
which to queens. The pupae of these three forms are easily distin- 
guishable and will be discussed in the order named. 



THE WORKER PUPA. 



(PI. IV, B, D.) 



The worker pupa immediately after transformation from the larval 
stage is pure white, without markings, except that the compound eyes 
are prominent as jet-black spots upon the head. The pupa is 
slightly larger than the grown larva, the average length bemg about 
2 mm. The head is by far the most prominent portion. A pupa 
measuring 2.04 mm. in length was found to have a head 1.19 mm. m 
length (dorso-ventral diameter), while the thorax and abdomen 
measured 0.51 and 0.561 mm., respectively. 

As time for transformation to adult approaches the pupa changes to 
a creamy color, then through a light brown to a dark brown, the latter 
shade being almost as dark as the body color of mature workers. The 
time of these changes varies with the duration of the pupal stage, but 
the following record of changes in color of a pupa which occupied a 
full 20 days from larva to adult (callow), is near the average: 

First to seventeenth day — Pupa pure white, except compound eyes. 
Eighteenth day — Turned to a light creamy yellow. 
Nineteenth day — Became a light brown. 
Twentieth day — The brown color deepened. 
Twenty-first day — Reached teneral stage. 



LIFE HISTORY. 



43 



In some colonies there is more or less of an indistinct sorting of the 
immature stages, pupae being placed in one portion of the nest and 
larvae in another. This tendency is not perceptible in many colonies 
and is usually most noticeable in very large colonies. 

The duration of the pupal stage has been determmed in the manner 
alreadv described for the incubation and larval periods. The range 
of pupal development is shown in the following table: 

Table IV. — Duration of pupal stage of the Argentine ant, individual ivorkers. 1908-9. 



Record No. 


From— 


To— 


Days.i 


Average 
daily 
mean 
tempera- 
ture 
during 
period. 


Average 
daily 
mean 

humid- 
ity. 


1 


Jan. 21,1908 
Mar. 14,1908 
Mar. 20,1908 
Mar. 30,1908 
Apr. 5,1908 
do 


Feb. 14,1908 
Mar. 27,1908 
Apr. 11,1908 
Apr. 14,1908 
Apr. 15,1908 
Apr. 18,1908 
Apr. 20,1908 
Apr. 23,1908 
May 13,1908 
May 14,1908 
Aug. 11,1908 
Aug. 16,19«8 
Aug. 20,1908 
Sept. 7,1908 
Ar)r. 28,1909 
June 22,1909 
July 0, 1909 


25 
14 
17 
10 
11 
14 
10 
16 
19 
20 
11 
11 
11 
11 
24 
10 
12.V 


° F. 
56.5 
67.5 
73.8 
73.8 
76 
76.3 
76.7 
76.6 
71 

71.2 
82.2 
83 

82.8 
81.4 
70.1 
82.75 
84.08 


Per cent. 
68.3 


2 


71.8 


5 


68.9 





70.2 


3 


73.5 


10 


74 


7 


do 


74 


8 


Apr 8,1908 
Apr. 25,1908 
do 


74.5 


9 


63.5 


11 


61.4 


4 


Aug. 1,1908 
Aug. 0, 1908 
Aug. 10,1908 
Aug. 28,1008 
Apr. 5,1909 
Juno 13,1909 
June 24,1909 


80 


12 


74.8 


13 


70.7 


14 


71 


19 


68.4 


21 .. 


68.75 


22 


76.08 







• Average days, 15. 

THE MALE PUPA. 

(PL IV, at center.) 

The male pupa is fully 50 per cent larger than the worker pupa and 
has, by comparison, an enormous thorax. The male pupae vaiy in 
length from 2.78 to 3.23 mm., with an average length of 3,04 mm.^ 
As the average length of the thorax alone is 1.19 mm., it is at once 
seen what a relatively large part of the body it constitutes. The male 
pupa is shown in the center of Plate IV. 

Wlien first transformed from the larval stage the male pupa is pure 
white, with exception of the compound eyes, which are faintly tinged 
with brown. Gradually the color of the compound eyes deepens and 
the ocelli become visible as minute dark spots upon the head. Ttie 
male pupa, like the worker pupa, passes through gradations of creamy 
yellow, light brown, and dark brown to almost black before transform- 
ing to the adult stage. The color reached by the male pupa just prior 
to transformation is much deeper than that attained by worker pupae. 
The males are assisted in their transformation to the adult stage by 

> From measurements of 10 specimens by Mr. Arthur H. Rosenfeld. 



44 



THE ARGENTINE ANT. 



the workers, and the pupal skm, or at least a portion of it, is worked 
backward to the tip of the abdomen and there shed entirely. Within 
a few hours after transformation the wings of the male become fully 
expanded. The following table shows the duration of the male pupal 
stage at different seasons. 

Table \ .^Duration of pupal stage of the Argentine ant, individual males, 1908. 











Average 












daily 


Average 










mean 


daily 


Record No. 


From — 


To- 


Days.i 


tempera- 
ture 
during 
period. 


mean 
humid- 
ity. 










- F. 


Per cent. 


1 


Apr. 11 

Apr. 14 

do. 


May 1 


19> 


73.6 


69.8 


2 


20,1 


73.6 


6S.6 


3 ... 


do 


20.1 
24' 


73.6 
72.3 


68 6 


4 


Apr. 17 
...do. . .. 


May 10 
.. .do. . . . 


67.3 


7 


24 
24 


72.3 
72.2 


67.3 


8 


Apr. 18 
...do 


May 11 
May 13 


66.7 


9 


26 


72.8 


66.5 


5 


Apr. 20 
Sept. 24 


do. 


24 


71.8 


65.8 


6 


Oct. 21 


28 


70.5 


67.8 







1 Average days, 2:i^. 

The normal time of appearance of the male pupge is in the spring, 
but the appearance of a relatively small number in autumn is not 
uncommon. During April and May they are usually abundant, 
gradually disappearing in the latter part of May and early June. 
Only in one case have they been observed in midsummer, when three 
or four male pupae were found at Baton Rouge, July 24, 1909, in a 
huge nest which contained thousands of immature stages. 

THE QUEEN PUPA. 

The pupa which is to become a queen is readily distinguished from 
the male or worker pupa by its size, as it is considerably larger than 
the male and more than twice as large as the worker pupa. The 
whole body is more uniformly developed than in the case of the male 
pupa. The head and thorax are not nearly so large in proportion to 
the rest of the body, the abdomen is much larger, and the dividing 
line between head and thorax is much more distinct. Apart from its 
size the queen pupa is readily recognized by the presence of the promi- 
nent wing pads. 

Queen pupae have been found only during April and May. The 
duration of this stage has not been worked out, as we have not been 
fortunate enough to secure larvae which would transform into queen 
pupae in our cages. Considerable numbers of these pupae have, how- 
ever, been collected in the field by the junior author and have been 
reared to the adult stage in the artificial formicaries, observations on 
them extending over a period of two weeks. The queen pupal stage 



LIFE HISTORY. 45 

seems to occupy relatively more time than is requli-ed for the worker 
pupal stage, but the gradual change in color from pure white to 
brown is about the same. It seems probable that the queen pupal 
stage extends over three or four weeks, depending upon the prevailing 
temperature. As many as 35 queen pupae were collected from one 
colony in Audubon Park, New Orleans, La., on April 29, 1910; hence 
there is every reason for believing that the virgin queens are reared in 
large numbers. 

Reasoning from what is known concerning the development of 
queens in the case of such insects as the honey bee, one would expect 
to find the queen ant developed from the same kind of an egg that 
produces the worker and that the queen would be developed as a result 
of special food given to the female larva. It is possible that the diet 
furnished to our colonies in confinement did not contain the requisite 
materials out of which the workers could elaborate a food suitable 
for rearing queens, and this may account for theii* failure ever to appear 
in the artificial formicaries, no matter how populous the latter were. 

THE CALLOW OR TENERAL STAGE. 

During the last few hours of the pupal stage, in all forms, the legs, 
mouth parts, and antennae become more prominent and the pupa is 
assisted in its transformation by the workers, who attempt to 
straighten out the legs and antennae. We are convinced that there 
is a very thin transparent membrane or skin surrounding the pupa, 
which is shed at time of transformation, but its existence is difficult 
to establish satisfactorily. 

Immediately after transformation the young ant is colorless, almost 
transparent, but is otherwise identical in appearance with fully 
mature specimens. To this stage, following the custom of some 
authors, wc apply the term "callow." The callow is at first very 
clumsy and walks with uncertain steps and staggering gait, reminding 
one much of a worker bee just emerged from the brood comb. During 
this stage the workers seem still to feel a responsibility for the cal- 
low's welfare, for when the colony is disturbed the callows, like larvae 
and pupae, are unceremoniously grabbed up by the workers and 
hustled to a place of safety. 

The body of the callow deepens in color quite rapidly and in from 
48 to 72 hours after transformation from the pupa becomes indistm- 
guishable from that of other adults. 

TIME REQUIRED FOR COMPLETE DEVELOPMENT. 

By adding together the minimum periods required for the develop- 
ment of worker eggs, larvae, and pupae, as given in Tables II, III, 
and IV, we find that at least 33 days are required for development 



46 THE ARGENTINE ANT. 

from egg to adult, and in a similar manner addition of the maximum 
periods gives 141 days as the maximum time required. 

From the tables also it is seen that the average period of incuba- 
tion of the eggs is 28 days, for development of the larvae 31 days, 
and for maturing and transformation of pupa to adult 15 days. 
By adding together these averages we arrive at 74 days as the average 
period of development. This, of course, can not be termed the time 
required for the development of a generation, since workers do not 
reproduce, and the term ''generation" can be used only in referring 
to the succession of queens. 

The time required for complete development of males is, of course, 
still unknown, for male larvae could not, in their earlier stages of 
growth, be distinguished from the worker larvae; while the larval 
form of the queen is still unknown. 

THE ADULTS. 

There are only three adult forms in the case of this ant, namely, 
the queen, male, and worker. Of the immature forms there are three, 
egg, larva, and pupa, of each the queen, male, and worker. There is 
hardly sufficient difference between the virgin queen and the dealated 
queen after fertilization to justify considering them as distinct 
forms. A complete colony may therefore consist of a queen and 
workers only, of queens and workers, or of a queen (or queens), 
males, and workers. With each of these combinations may be asso- 
ciated any one or more of the tlu-ee immature stages, corresponding 
to each of the three adult forms, or nine immature stages in all. 
Plate II shows a colony consisting of 1 queen, about 100 workers, 
and about 20 eggs, with no larvae, pupae, or males present. For a 
technical description of these adult forms the reader is referred to 
other pages. The following descriptions are general in their nature: 

The Worker. 

The worker measures from 2.25 to 2.75 mm. in length and is well 
illustrated at h, figure 6. As with the queen, the abdomen extends 
to about the tarsi of the hind legs when the worker is active or engaged 
in feeding. The abdomen is capable of considerable distension, and 
when the worker is fully engorged with sirup or other liquid its 
chitinous plates are forced apart, rendering the connecting mem- 
branes distinctly visible. The writer has often noticed workers 
returning from their attendance upon plant lice with abdomens so 
distended that they looked like little drops of silvery liquid. Par- 
ticularly is this appearance presented when the returning workers 
are viewed with a strong light beyond them. 



LIFE HISTORY. 47 

As would naturally be expected in the case of so small a creature, 
the weight of a single worker is very small. To determine it, 1,000 
workers, freshly captured and killed with cyanid fumes, were care- 
fully counted and weighed on an analytical balance. The thousand 
insects weighed 0.2077 gram, which gave the average weight of each 
worker as 0.0002077 gram, or two-tenths of a milligram. 

As already stated, there is only one caste among the workers. In 
a large colony there seems to be something of a division of labor, 
certain ones engaging in foraging, others in nursing, and still others 
in excavating or sanitary work. However, any individual worker 
can assume the duties of any other, and does do so when exigencies 
demand. Worker callows, barely hardened into mature adults, go 
forth in search of food and the hardened veterans of many months' 
service seem to make as efficient nurses as even the youngest, 

LENGTH OF LIFE. 

The workers are particularly long lived. A colony of about 70 
workers was made queenless and broodless on July 8, 1908. By 
October 10 the number of workers had become reduced to about 40, 
and some of the original ones survived until February 25, 1909, a 
period of 6^ months. As tills colony was queenless, the workers in 
it were not under normal conditions. With a queen present it is 
ordinarily impossible to ascertain the length of life of individual 
workers, owing to the constant maturing of young. However, in 
one case we had opportunity to observe the survival of workers with 
queen present and with immature stages absent. A colony started 
on October 10, 1908, proved to have an infertile, dealated queen 
and was kept under observation to see how long the workers would 
survive. The last of these died on July 22, 1909, having lived for 9 
months and 12 days after their capture. Their age at the time they 
were confined in the cage on October 10 was, of course, unknown; but 
it appears safe to conclude that under normal conditions the workers 
not infrequently live to an age of at least 10 or 12 months. 

Mr. G. D. Smith was successful in keeping a queen and several 
workers for more than two months, during which time they had no 
food other than that which may have been contained in the drinking 
water furnished them. During this period of prolonged fasting the 
queen even deposited eggs, some of which hatched into larvae. 

The Male. 

The appearance of the adult male is illustrated at a, figure 6. The 
males average about 2.8 to 3 mm. in length. The most noticeable 
feature about them is the manner in which the thorax is enormously 
developed. The abdomen is relatively small and the head short 



48 THE ARGENTINE ANT. 

and blunt. The shape of the head alone permits distinction between 
the male and virgin (winged) queen without the aid of a glass. 

The normal time of appearance of the males, of course, follows the 
appearance of the male pupse, usually in the spring, but a few appear 
in the fall. They are plentiful in the colonies during the latter part 
of April and May, and numbers are still to be found in June. After 
the beginning of July, however, they vanish, and are very seldom 
seen during the hot months of the summer. A few are occasionally 
found during October, November, and December, and in one case 
a few males were found in a colony as late as January. 

The males are essentially drones, and never exhibit any indications 
of industry or usefulness beyond their special function. 

The Queen. 

Adult queens are found in two forms, the winged and the wingless 
or dealated. The former is the virgin cjueen and the latter the fertile 
or egg-laying queen. 

THE VIRGIN QUEEN. 

When the queen reaches maturity she possesses long narrow wings 
which are rather opaque, gray in color, with the veins and stigma 
pale brown. In other respects she does not differ in appearance 
from the dealated cjueen, described on page 49. The wings are 
retained until after the queen has mated. Mating may take place 
during the nuptial flight in spring, but under some circumstances 
occurs within the nest without any flight being made. In the latter 
case the queen loses her wings shortly after fertilization and assumes 
her egg-laying duties in the home nest along with the older queens 
already there. 

The earliest date at which we were able to find virgin queens in the 
outdoor colonies was April 1. Normally the first spring appearance 
of males precedes the first appearance of virgin queens by about 
three weeks. 

Probably owing to the extreme shortness of the winged stage, 
winged queens are very hard to find in the outdoor nests. Although 
they must exist in large numbers every spring, they have been col- 
lected only occasionally. Most of our observations have been made 
upon specimens reared from pupse in artificial nests. 

An enormous and general flight of males and virgin queens was 
observed at Baton Rouge, La., in the spring of 1908, when large num- 
bers of both sexes were captured in butterfly nets. On the other 
hand, during the spring of 1910 and that of 1911 no general flight 
was observed at New Orleans, La., although close watch was kept for 
one. Considerable numbers of males were seen flying around the 
city electric lights, and individual males were found flying aimlessly 



LIFE HISTORY. 49 

in various localities, but no queens were found with them, and no 
flight took place that could compare with the one noted at Baton 
Rouge in 1908. 

At the same time a large number of queen pupae transformed into 
winged queens in a large Janet style nest in the laboratory at Audu- 
bon Park, New Orleans, La. About an equal number of males were 
also present in the same nest, which the junior author watched 
closely for a flight. Nothing of the kind took place. On two occa- 
sions all ants were driven out of the nest — workers, males, and queens — 
to see if they could be induced to fly, but after wandering around for 
a time they all returned to the nest. The males could be seen actively 
pursuing the young queens inside of the nest, and although copulation 
was never actually observed, it must have taken place. In the course 
of time all the queens lost their wings and commenced to lay an 
enormous number of eggs. These eggs hatched, and finall}^ developed 
into workers, proving that they were fertile. The males all died one 
by one, the last one disappearing when about two months old. It is 
therefore evident that the nuptial flight is not a necessity. 

Under natural conditions the tendency toward a general flight may 
be partially controlled by the comparative numbers of males and 
young queens in the nests and colonies. The weather conditions 
about flying time may also exercise a very important influence upon 
the flying impulse; cool, cloudy, and rainy weather tending to 
restrain the inclination to flight, and warm, clear weather encouraging 
it. The severity of infestation may also be an important factor, as 
the ants would be more likely to fly in crowded communities than in 
localities where they are comparatively scarce. 

The males are much more given to fhght than the virgin queens. 
In the formicarium at Baton Rouge males were often found flying 
during their season, and seemed to have no preference as to time of 
flight. They were found flying on cloudy days as well as on clear 
ones and as frequently at night as in the day. 

THE DEALATED, OR FERTILE, QUEEN. 

The dealated queen is illustrated at c, figure 6. The dealated 
queen measures from 4.5 to 5 mm. in length, and queens measuring 
6 mm. in length are not uncommon. It should be remarked here that 
during egg-laying periods the abdomen is much larger and longer 
than shown in the drawing. Normally the abdomen extends well beyond 
the tarsi of the hind legs. Unfortunately, a drawing can not show 
the delicate silky pubescence of the queen's body, and in life she is a 
far more beautiful creature than one would imagine from the drawing, 
correct though the latter is in anatomical detail, 
75508°— Bull. 122—13 4 



50 THE ARGENTINE ANT. 

The credit for first discovering and recognizing the queens of this 
species seems to belong to Mr. E. Baker, formerly superintendent of 
Audubon Park, New Orleans, and Prof. R. E. Blouin, formerly in 
charge of the Audubon Park Experiment Station. 

The rate at which the queen deposits eggs varies with the prevail- 
ing temperature, and egg deposition is suspended entirely at low tem- 
peratures. In the artificial formicaries, already described, the num- 
ber of eggs laid each day varied from 1 or 2 to as many as 50 or 60. 
Thirty per day is not far from the normal number in warm weather, 
when the food supply is abundant. It appears probable, however, 
that the queens deposit much more rapidly in large colonies, although 
from the nature of the case this can not be verified by direct observa- 
tion. Egg deposition becomes Very slow, or ceases entirely, in the 
artificial formicaries when the daily mean temperature falls below 
68° F. 

Practically all queens under observation have shown a disposition 
to suspend egg deposition entirely for longer or shorter periods, even 
when the occurrence of such periods can not be accounted for by low 
temperatures. 

Fertile queens confined in test tubes without accompanying 
workers will often deposit a few eggs upon the walls of the tubes, but 
we have been totally unable to get colonies established by confining 
queens in artificial formicaries without workers accompanying them. 
This failure has not been due to any need of workers to feed or care 
for the queen, since she can feed herself from a supply of honey or 
sugar as readily as can a worker. Ordinarily she attends to her own 
toilet, and it is doubtful whethef she is in reality "attended" by the 
workers in the sense that queen bees are attended. 

Fertile queens do not confine themselves to the formicaries, either 
natural or artificial. Isolated dealated queens are not infrequently 
found wandering about buildings by themselves, and while the queens 
in artificial formicaries ordinarily stay within the nest proper, they 
have at times been seen outside of it. The finding of dealated queens 
wandering about, coupled with the fact that workers readily accept a 
queen from any source, seems to indicate that new colonies may 
sometimes be established in nature by workers associating with such 
wandering queens. 

The length of life of the queen has never been determined, but 
there is no doubt that it extends over several years. Observations 
have been carried on with the same queen for considerably over a year. 

The number of queens that may be found in a colony varies from 
one to several in the summer nests, and may reach into the hundreds 
in the large winter colonies. Queens never show the least hostility 
to each other or to the workers. 



THE COLONY AS A WHOLE. 51 

In the laboratory at Baton Rouge it was our custom to put all sur- 
plus queens into one colony, kept for the purpose, and leave them there 
until wanted. As many as several dozen queens were sometimes in 
this colony at once, all living peaceably together, and with the num- 
ber of queens sometimes exceeding the number of workers. 

Queens will frequently leave the nests with the workers, and will be 
observed in the foraging trails. Ten queens were collected in 30 min- 
utes from a large trail of workers at New Orleans, La., during Jan- 
uary, 1911. These were quite remote from the nearest nest. Any 
colony will immediately accept a strange queen without hesitation, 
and it is probable that a constant interchange of queens takes place 
between different colonies. 

THE COLONY AS A WHOXE 

In size the colonies may vary from a dozen to many thousands of 
individuals and the number of queens present in a colony may vary 
from one to many hundreds. Although the Argentine ant is particu- 
larly aggressive and a hard fighter when coming in contact with most 
other species of ants, there is no apparent antagonism between sepa- 
rate colonies of its own kind . In fact , in heavily infested areas the work- 
ers and queens are so intermingled that the individuality of colonies 
is entirely lost sight of and all colonies appear to become part and 
parcel of one enormous community. In this respect the species may 
be said to have a more perfect social organization than even the honey 
bees, colonies of which are very distinct and the individuals of which 
usually repel with alacrity any visitor from another colony. 

SEASONAL HISTORY. 

In order to connect the scattered and individual life histories 
already given into one united whole it may be well to take a glance at 
the changes which occur in the ant colonies with the different seasons. 

WINTER COLONIES. 

The tendency of the Ai^gentine ants to segregate into large winter 
colonies is very pronounced, and during the winter small colonies 
are very scarce, while nearly every protected situation will reveal 
the presence of enormous colonies. The stages which are represented 
in the nest are queens, workers, eggs, larvae, and worker pupae. 
During cold weather very few changes occur. The egg and larval 
periods are very much lengthened compared to the summer rate of 
development. The workers themselves move very little, and a large 
colony will subsist upon a small supply of food for long periods. 
During warm days heavy trails of workers emerge from the nests 
and carry back anything available for food. Except for this the ants 
may be considered as almost in hibernation during the winter months. 



52 THE ARGENTINE ANT. 

When the temperature falls as low as 60° F. the ants become 
sluggish, and foraging is largely suspended. At from 50° to 55° F. 
there is practically no foraging, and when this temperature is reached 
within the nest all adult ants become inactive, moving only occasion- 
ally, and even then with apparent difficulty. Activity is not strictly 
limited by these temperatures, however. On one occasion we found 
workers foraging in a building the interior of which was at 43° F., 
but the colony itself was outside the building and at a higher tem- 
perature. Very few refrigerators are cold enough to keep out these 
invaders when the outside temperature is warm enough for them to 
forage normally. On the very hottest days of summer they will 
enter refrigerators and even crawl into the ice chamber itself in order 
to reach some much-desired delicacy. 

The most ideal location for the large \vuiter colonies is in piles of 
decomposing vegetable matter. This material gives off a large quan- 
tity of heat during the process of rotting and consequently furnishes 
the ants with automatically heated apartments. In the same manner 
in which the ants seek optimum humidity conditions during the 
summer months, so they will regulate their location to preserve an 
even temperature in their nests in the winter. In cold weather they 
will carry the young stages toward the center of the piles, while in 
warmer weather they will be found near the surface. 

Of course all the ants are not able to find ideal locations for the 
winter months, and great numbers have to locate themselves as well 
as they can. In open fields great numbers will be found under large 
ridges, or along ditch banks, particularly those which have a southern 
exposure. Many will burrow mto the ground at the bases of large 
trees, where their tuimels and galleries will sometimes attain a depth 
of 12 to 14 inches. 

Under Louisiana conditions the winter colonies are in evidence 
durmg the months of December, January, and Febmary. The segre- 
gatmg tendency becomes marked during November, and the '^ divis- 
ional migration" normally occurs in February, but may not take 
place until March if the spring is cold and wet. 

SUMMER COLONIES. 

As soon as the weather gets warmer in the spring and food becomes 
abundant the large winter colonies break up into a great number of 
smaller colonies. These usually consist of one or more queens and a 
considerable number of workere, and they establish themselves in 
any good location where a supply of food is available. In places 
where food is exceptionally abundant these summer colonies will still 
remain very strong in numbers. Under large magnolia or oak trees, 
for example, colonies with 10 or 20 queens and many thousand 
workers are nearly always present. 



THE COLONY AS A WHOLE. 53 

A short time after the ''divisional migration" has taken place in the 
early part of March, the large amount of food brought in by the 
workers, acting in conjunction with the warmer temperature, appears 
to stimulate the queens to lay great numbers of eggs. Most of the 
young stages carried through the winter or which have slowly matured 
during winter have by this time transformed into workers, so that 
the colonies consist of many workers, with comparatively few imma- 
ture stages other than the eggs. Hatching takes place during the latter 
half of March, and the larvae resulting from these eggs, after develop- 
ing, transform into three classes of pupae, viz, queen, male, and 
worker. Of these the male pupae preponderate, with the workers a 
close second and queen pupae a very poor third. The male pupae 
appear in great numbers several days before the queen pupae appear, 
which may possibly indicate a slightly longer larval period for the 
queens than for the males. 

The adult winged males appear during the latter part of April and 
in May, and are in evidence in the nests until the beginning of Jime, 
when they begin to disappear. The winged queens appear a few days 
later. For some reason the winged queens are extraordinarily diffi- 
cult to find in the nests, although their large size and long narrow 
wings should make them very conspicuous. However, only three 
winged queens have as yet been located in the nests under natural 
conditions in Louisiana. Fortunately the queen pupae are not so 
difficult to discover, and a considerable number have been reared to 
the adult stage in Janet style nests in the laboratory, where most of 
our observations upon this stage have been made. 

The appearance of the winged queens and males may or may not 
be followed by a nuptial flight. In either case, after the queens have 
become fertile they lose their wings and immediately start laying 
great numbers of eggs. These eggs develop into workers, with the 
exception of a few eggs which are laid in the late autumn and develop 
into males. It thus follows that the most rapid and conspicuous 
increase in numbers occurs during July, August, and September, 
when the eggs laid by the army of young queens complete their life 
history and transform into adult workers. 

From then on to late in the fall the history of the colonies is very 
similar and devoid of incident. The numerical strength of the ants 
is constantly on the increase, and it is probable that the greatest 
natural dispersion occurs during the fall months, after the nests 
have been excessively crowded by the activity and increase of the 
summer. 

During the latter part of October and in November the nights 
begin to get cool and we find the first inclination toward the form- 
ation of the winter colonies. The nests in exposed open situations 
are gradually deserted, and strong colonies accumulate m well- 



54 THE AEGENTINE ANT. 

protected situations. This becomes more pronounced during the 
latter part of November, and in the beginning of December we find 
'that the winter colonies with which we began are once more restored 
and that large united colonies are the rule, with small colonies the 
exception. 

COMPOUND COLONIES OR COMMUNITIES. 

Mention should not be omitted of the pronounced manner in which 
the social habit is extended beyond the limits of the individual nest 
or formicary. During the summer season of activity, and in heavily 
infested areas, communication between adjacent colonies is com- 
monly observed. Not only the workers, but even fertile queens, 
travel from one colony to another. So closely are adjacent colonies 
associated in their activities that one can not do otherwise than con- 
sider a heavily infested area as one enormous ''compound colony" or 
community. 

MIGRATIONS. 

Four distinct types of migration are exhibited by these ants, 
without includmg the long trips which they take in columns to and 
from the nests in search of food. 

GENERAL MIGRATION OR DISPERSION. 

By general migration is meant the slow but steady spread of the 
ants from infested points into adjacent uninfested territory. This is 
practically continuous, and while under natural conditions it may 
amount to only a few hundred feet per year it is greatly accelerated 
by artificial dissemination of the ants by man and his agencies. 

MIGRATION TO POOD SUPPLY. 

When the supply of food becomes scarce in the immediate vicinity 
of a colony and a plentiful supply is discovered at a distance by the 
foraging workers, movement of the colony in toto to the neighbor- 
hood of the latter is not infrequent. Trees or plants harboring large 
numbers of scale insects are invariably surrounded by many populous 
colonies and the housewife who grows careless, permitting the ants 
to get food in plenty within her domicile, is soon repaid by having 
the premises overrun with the pests. One can easily note this form 
of migration by keeping a constant supply of honey or sirup in one 
place for several days and providing a suitable nesting place — such 
as a decaying log — near it. The latter is shortly occupied by one or 
more colonies. 

CONCENTRATING MIGRATION. 

Concentrating migration takes place within the infested territory 
and consists of the coming together of a large number of smaller colo- 
nies to form a single large colony. This migration occurs under 



THE COLONY AS A WHOLE. 55 

various adverse conditions. During floods tlie ants will concentrate 
in great numbers upon elevated ground, or many colonies will carry 
theii' young stages up the same tree in order to get protection from 
the rising water. The most pronounced concentration, however, 
occurs at the approach of cold weather in the fall, when large numbers 
of colonies concentrate at one point to form the large winter colonies, 
often consisting of hundreds of queens and many thousands of work- 
ers. These colonies are fully described elsewhere. 

DIVISIONAL MIGRATION. 

Divisional migration is the opposite of concentrating migration, 
and is always in evidence after a large number of ants have conce .- 
trated at one place. It is most conspicuous in the spring, when the 
large whiter colonies break up into a great number of smaller ones. 
These small colonies usually consist of one or more queens and a sup- 
ply of workers. They distribute themselves in all directions from the 
large colony, and locate in any place which affords suitable protec- 
tion and an available food sup])ly. 

NESTS OR NATURAL FORMICARIES. 

Almost any place seems to be suitable for the location of nests of 
the Argentme ant, provided that light and water may be sufficiently 
excluded. Some of the situations in which they have been found 
are within hollow trees, beneath the rough bark of growing trees, 
in forks of trees, in rubbish and compost heaps, in decaying logs and 
timbers, beneath boxes and boards, under and in brick foundations, 
in stored household goods, beneath shingles on roofs, in rolls of wrap- 
ping paper, betv/een walls of dwellings, in flowerpots, in piles of 
brick and stove wood, in garbage cans, in bags of sugar, in birds' 
nests, in discarded tin cans, in moss packing about the roots of nur- 
sery stock, and in straw packing containing glassware or china, in 
beehives with colonies of bees, under discarded tin roofing, around 
the roots of cotton, corn, sugar cane, and other growing crops, in 
railway cars, in various places on river steamboats and ocean-going 
vessels, in old clothes, under street-car tracks, under brick and con- 
crete pavements, in greenhouse benches, inside the husks of roasting 
ears, inside of cotton bolls, in hollow iron electric-light posts, in the 
cracks and crevices in telephone and telegraph poles, and in the cinder 
ballast of railroad tracks. 

Most of the situations named are used as permanent nesting places 
so long as weather conditions do not force the ants to find more 
suitable quarters. With the advent of unfavorable conditions the 
ants move theu" colonies with alacrity. 



56 THE ARGENTINE ANT. 

Many permanent nests are located in the tops of trees, in rotten 
branches, or in places where borers or termites have been working. 

In rotten logs the ants wUl nearly always utilize old borer or termite 
tunnels for their nests, but do not appear to do any boring for them- 
selves. 

The facility with which entire colonies move is sometimes amazing. 
If a nest is disturbed the workers will frequently move all stages and 
establish another nest in a fresh location in the course of a very few 
minutes. 

UNDERGROUND NESTS. 

The ants seldom burrow to any great depth in the ground. The 
exceptions to this occur during hot, dry weather m the summer or 
durmg particularly cold spells in the winter. In the dry spells they 
evidently work downward in an endeavor to secure sufiicient hu- 
midity for the young, while in the wintertime they sometimes go 
deep mto the soil for the sake of protection from the cold. The 
deepest burrows which we have measured have been 14 inches in 
depth, but they usually average from 4 to 10 inches under normal 
conditions. These deep burrows are usually located at the foot of 
tree trunks, or under the ridges in cane, cotton, or corn fields. 

Under more favorable circumstances, however, the underground 
galleries average from 1 to 4 inches in depth. In summer time the 
ants appear to do as little excavating as possible and seem to limit 
their efi^orts to excluding light and water. When the nests are 
located above ground, under boxes, boards, stones, etc., very little 
soil is used, and this is utilized in closing holes, etc., to keep out 
light and drafts. 

WET-WEATHER NESTS OR SHEDS. 

In wet situations or after heavy rains, when the ground has become 
soaked with water, the ants construct curious honeycombed structures 
around the bases of tree trunks. These are made of a great number 
of fine, loose particles of soil, usually supported by grass stems or 
loose leaves. They vary from one-half inch to as much as 5 inches 
in height, and sometimes cover an area of several square feet. They 
are built with great rapidity by the workers, and are extremely frail, 
falling in at the lightest touch. As a result of this weakness these 
nests disappear after a few days of dry weather, or are washed away 
by showers. They consist of a maze of covered galleries, in which 
large numbers of the larvae and pupae are placed. Their purpose 
appears to be to aftord protection to the young stages until the 
ground gets dry enough for the underground galleries to be 
reoccupied, or they may be used to dry and ''air" stages which 
have become wet, the loose construction permitting a liberal circula- 
tion of the air through the walls and ceilings. (See PI. V.) 



Bui. 122, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate V. 




Wet-Weather Nest or Shed, Erected by Argentine Ants During Rainy Weather. 

(Original.) 



THE ARGENTINE ANT. 57 

GENERAL OBSERVATIONS. 

AVERSION TO LIGHT. 

The ants demonstrate in many ways their dislike of light, or at 
least their aversion to it. Their nests are always located in dark 
places, the ants are active all night, and their immature stages are never 
exposed to light except for brief periods in emergencies. If the 
opaque cover is removed from the top of an artificial ant nest for a 
considerable time, all the ants will come out and will refuse to return 
until the cover is replaced. Several experiments were made at 
Baton Rouge, La., in 1909, using different colored glasses for cage 
covers, but the ants were not satisfied unless the cover was absolutely 
opaque. While they will go anywhere into daylight in search of 
food, they will cover over as thoroughly as possible, with their 
protective "sheds," the colonies of scale insects, mealy-bugs, and 
aphides which they habitually frequent. 

SENSE OF SMELL. 

The workers exhibit a very keen sense of smell by the manner 
in which they locate certain foods. Meat which is wrapped in heavy 
wrapping paper will attract thousands of the insects, and they will 
work their way through the various folds and crevices of the paper 
in a surprising manner until they reach the meat itself. The workers 
readily secure entrance into the ordinary Mason or glass fruit jar, 
if one omits placing beneath the cover the rubber ring or gasket. 
No matter how tightly the cover is screwed on, the workers follow 
the spiral threading between cover and glass until the interior is 
reached. 

Another illustration of the sense of smell is seen in the readiness 
with which trails are restored when broken or disturbed. If a line 
of ants be moving across a floor in a circuitous line, for example, 
and all ants be swept from the floor with a broom, the next on-coming 
workers will follow exactly the original course. This may be repeated 
indefinitely and the trail will always be established in the original 
location. If, however, some strong-smelling substance, like oil of 
citronella or kerosene, be placed upon the trail the ants become 
confused at once and by their aimless wandering about show plainly 
that they can not locate the original pathway. 



While the Argentine ants are extremely sensitive to light, it is 
doubtful if they possess the sense of sight. The action of light can 
generally be described as exerting a repelling influence upon them 
and they avoid it as much as they can. That they do not use eyesight 
in locating food substances has long been recognized. Their trails 



58 THE ARGENTINE ANT. 

will frequently encircle the spot which they ultimately hope to attain. 
They will never attempt to avoid a hand threatening from any 
direction as a spider will do, but will continue going ahead until 
their antennae touch the obstacle. The manner in which they 
religiously follow their trails and the confusion which results when 
these trails are destroyed proves that they do not trust to a sense of 
sight in traveling. This is illustrated again by the fact that they are 
active all night in the darkest situations. 

HEARING. 

The sense of hearing in these insects is not acute, even if indeed it 
be developed at all. The ants are not disturbed by ordinary noises, 
such as talking or working about the nests. If, however, one emits 
a loud shout within a few inches of the formicary, or fires a pistol 
near it, the ants are thrown into the confusion and excitement 
characteristic of them when disturbed. It seems not impossible 
that in such cases they have detected actual vibrations of the surface 
on which they are located, due to the action of the sound waves. 
Strangely enough, in situations where loud noises and vibrations are 
of constant occurrence, the ants become accustomed to them. Thus 
at New Iberia, La., we found ant colonies between and under the 
ties of a railroad track over which many trains passed daily. 

CANNIBALISM. 

CannibaUsm in any form is extremely rare in the case of this 
species, and true cannibalism has not yet been observed. The only 
thing at all approaching it was observed in the case of a colony kept 
in our formicarium, the workers of which developed a habit of eating 
the eggs as fast as they were deposited by the queen. This colony 
was established in an artificial formicary on November 27, 1907, and 
from that time until the early part of July, 1908, larvas were reared 
more or less continuously and in the usual numbers. In July it was 
noticed that the nmnber of immature stages became steadily smaller, 
and on July 28 a quick removal of the cover from the cage disclosed 
several workers in the act of eating eggs. Thinking that this might 
be due to lack of sufficient food of an animal nature fresh meat was 
at once furnished the colony and was thereafter kept continually 
accessible. In spite of this the egg-eating habit continued until 
November 5, 1908, all eggs being eaten Nvithin a few hours after their 
deposition by the queen. By this time the number of workers in the 
colony had been reduced to six, and by November 1 1 the queen and 
remaining workers were dead, the colony having apparently been 
exterminated through lack of any maturing workers to replace those 
dying from old age and accident. 



GENERAL OBSERVATIONS. 59 



SANITATION. 



All adult members of the colony keep themselves scrupulously 
clean, after the manner of most hymenopterous insects. Workers 
divest then- bodies and legs of foreign matter by persistent rubbing 
of the body and antenna? %\dth their legs, while the tarsi are cleaned 
by pulling them between the mandibles. At times we have seen the 
workers assisting each other in these operations, particularly when 
some gummy or adhesive sul)stance ])ecame attached to the head and 
mandibles. On one occasion the senior author observed one worker 
industriously cleanmg the mandil^les of a companion. During this 
operation, which lasted for several minutes, the worker receiving the 
kindly ministrations stood with her head well raised, mandibles 
extended, and feet firmly braced, while the teeth of her mandibles 
were thoroughly cleaned by those of her sister. 

The queen is occasionally^ cleaned and groomed by the workers, 
but for the most part she attends to her own toilet, being nearly as 
skillful and dextrous at the task as are the workers themselves. 
Larvae and pupae are groomed from tune to time, this grooming being 
done with the tongues of the workers. 

Dead adults or larvae are not tolerated ^nthin the colony and are 
removed immediately. Dead adults are also invariably removed 
from the vicinity of any food supply which the ants are visiting. 

Decaying animal matter is not tolerated in near proximity to the 
nests. If the ants are unable to remove it bodily they wiU carry 
particles of earth with which to bury it, much after the manner 
adopted by honey bees in covering with propoUs any dead animal 
which they can not remove from their hives. The following example 
will serve to illustrate this habit: A small minnow, recently dead, 
was placed near the entrance of one of the artificial formicaries. It 
was immediately covered ^^'ith workers, and in the course of a few 
hours aU the soft portions had been torn apart and carried into the 
formicary, little remaining except the bones and skin. On the fol- 
lowing day another fresh minnow was given the' same colony. Wliile 
this was torn apart the same as the first one, it did not receive nearly 
as much attention. Wlien a third minnow was given the colony the 
workers paid no attention to it, having evidently had fish "a plenty." 
As soon as it commenced to decay the workers brought particles of 
trash and dirt from their nest and piled these up around the minnow. 
This work they continued for three days, by the end of which time 
the remains of the minnow were completely buried. Decaying fruit 
left near the artificial nests was treated in the same manner. 

RATE OF TRAVEL. 

One of our associates, Mr. G. D. Smith, made some interesting 
experiments to determine how rapidly the workers travel both in 
going to food and in returning from it with their loads. Sirup was 



60 THE ARGENTINE ANT. 

placed on the comparatively smooth floor of an infested building, 
and when the ants were visiting it in large nmnbers a distance of 
6 inches was measured off on one of the principal "trails." The rate 
of travel of individuals over this 6 inches was then noted. Mr. Smith 
found that the average time required to travel the 6 inches when 
going to the food supply was 12^ seconds, or at the rate of 29 inches 
per minute. When returning from the food, presumably with their 
stomachs filled with sirup, the average time required to travel the 
G inches was 21 seconds, or at the rate of 17 inches per minute. The 
rapidity with which the foraging ants can travel (29 inches a minute, 
or 145 feet per hour) explains their ability to keep thoroughly 
patroled all of the walls, furniture, and other contents of a building 
within their reach. It explains at the same time the reason for their 
so quickly locating food supplies left accessible to them. 

The rate of travel over horizontal polished surfaces is, however, 
much greater than that cited above. On a tiled floor or on the top 
of a glass showcase their speed is two or three times as great as that 
just given. In fact, it is ahnost impossible to capture the workers 
on a tiled floor, so rapidly do they move. This same degree of speed 
is not attained on vertical polished surfaces, such as window panes. 

STORAGE OF FOOD. 

Only to a very small extent do the workers of this species provision 
their nests for future emergencies. They are given to carr^-ing let- 
tuce seed, and perhaps other seeds, into their colonies at times, but 
the bulk of these seed are used up in a short time, and in a few days aU 
have disappeared. Apparently the desire to carry in a full supply of 
any desirable food is the cause for this storage, rather than any fixed 
instinct toward providing the colony vnih permanent stores. In like 
manner, when the ants have access to large amounts of granulated 
sugar, the granules are carried into the nest and deposited in various 
parts of the galleries, -there being no place set aside, apparently, as a 
granary or storehouse. Like the seeds above mentioned, the supply 
of sugar is consumed wdthin a few hours or a few da^^s after its 
acquisition. Particles of meat are deposited in the galleries in simi- 
lar manner, often to be neglected until they are too dry to be of much 
service. Even when dried, however, they seem to furnish a relish or 
variation in the diet, as workers may be seen, from time to time, 
rasping off small shreds with their mandibles and then masticating 
these with apparent enjoyment. 

Liquid food, such as honeydew, sirup, etc., is not deposited any- 
where in the nest, and if any liquid food is kept in reserve at all it is 
merely that which is retained in the stomachs of the workers. Appar- 



EELATIONS WITH OTHER ARTHROPODA. 61 

ently liquid food is consumed soon after being brought into the for- 
micary, as evidenced by the following observation : 

Some fresh honey was placed upon the food table of an artificial 
formicary, and when the first worker was observed to leave the honey 
the top of the formicary was removed and her actions observed. 
Upon entering the colony she was met by three other workers, all 
of which placed their mandibles to hers. As she regurgitated the 
liquid they sipped it up. When one of these workers had received a 
sufficient quantity she retired and another took her place, as many 
as four or five workers sometimes feeding at once. The foraging 
worker in this manner supplied about 15 others with food, after 
which, her supply being apparently exhausted, she left the group of 
assembled feeders and went her way, leaving some of them hungry 
and still unsatisfied. 

RELATIONS WITH OTHER ARTHROPODA. 
FORMICID^. 

It may be said in general that the Argentine ant wUl not tolerate 
the presence of other species of ants within its domains. There are 
a few exceptions to this rule. - In 1908 IVIr. G. A. Runner and the 
junior author found a small colony of Monomorium minimum Buck- 
ley living in the same tree stump with a colony of Argentine ants at 
Baton Rouge. The Monomorium colony possessed a number of young 
stages and appeared to be unmolested by the Argentine ants. The 
following season, however, the Argentine ants were in full possession 
of the stump, and no trace of Monomorium could be found. During 
the same summer another small colony of M. minimum was noticed 
living in a fig tree in territory heavily infested with the Argentine 
ant. This was also at Baton Rouge. This colony was observed for 
several weeks, but finally died out, though it could not be determined 
whether the Argentine ants were responsible for its annihilation. 

In another case a log was split open, disclosing vigorous colonies 
of both Iridomyi'mex humilis and M. minimum. Whether the ants 
were occupying the same chambers or whether the nests were in 
close but disconnected chambers could not be ascertained, but the 
Monomorium workers were seen to pick up and carry away the larvae 
of humilis with as much solicitude as they did their own. Just what 
relationship obtains between these two species we have not been 
able to determine, but certain it is that humilis tolerates this small 
species to a much greater extent than it does any other ant. At 
Baton Rouge Monomorimn tninimum still seems to maintain its 
normal abundance, and this certainly can not be said of any other 
species of ant. 



62 THE ARGENTINE ANT. 

An account of the methods used by the Argentine ants in over- 
coming other species of ants was published by the senior author ^ 
in the Journal of Economic Entomology. 

Prof. W. M. Wheeler, in Entomological News for January, 1906, 
gives an interesting account of the way in which this species obtained 
a foothold in Madeira and supplanted another introduced species, 
Pheidole megacephala Fabr, 

COCCID^ AND APHIDID^. 

The liquid excretions of the various species of scale insects and 
aphides form one of the chief sources of food for the Argentine ant. 
The large variety of trees and plants in the South gives support to a 
great number of coccids and plant lice, and these insects in turn 
yield sustenance to myriads of ants. In return for this food supply 
the ants shelter and protect these insects, with the result that the 
latter mcrease beyond all customary proportions. As the result of 
this symbiotic manner of living we find that a comparatively small 
area of land frequently supports enormous numbers of ants, scale 
insects, and aphides, while the plants themselves become so severely 
infested that some of them are killed and many more seriously 
injured. 

All through the summer months, and also during warm days in 
winter, heavy streams of ants can be seen ascending and descending 
the trees and plants; the ascending ants empty, the descending ones 
heavily laden with the liquid excretion which they have obtained 
from the various scale insects and plant lice. Durmg the summer 
this activity is well-nigh endless, and the ant trails can be observed 
at all hours of the day and night. All scales and aphides are closely 
attended, but some species appear to attract more of the ants than 
do others. The large unarmored scales and the plant lice appear to 
be the chief favorites, the mealy-bugs, however, following them very 
closely in this regard. 

Aside from protecting the aphides and scale insects from ladybird 
beetles and constructing earthen shelters over them, the ants only 
rarely foster them directly. In one case only have insects of this 
character been actually found in the ants' nests. In January, 1909, 
Air. G. D. Smith, in excavating an underground colony at Baton 
Rouge, found a number of barnacle scales, Cewplastes cirripediformis 
Comst., on tree roots which passed through the formicary. These 
scale insects were fuU grown and vigorous. At this season of the 
year no live scales of this species could be found above ground. It 
may be remarked in passing that this is one of the species to which 
the ants are very attentive during the summer and autumn months. 

1 Notes on the Habits of the Argentine or "New Orleans" Ant, Iridomyrmex humilis Mayr. WUmon 
Newell, Journ. Econ. Ent., vol. 1, no. 1, pp. 21-34, 1908. 



EELATIONS WITH OTHER ARTHEOPODA. 63 

Workers are often seen carrying plant lice and scale insects, and 
this fact, coupled with the observed phenomenal spread of scales in 
ant-infested territory, brings one inevitably to the conclusion that 
the workers carry and establish these pests upon new growth and 
upon new host plants. 

During March, 1910, a considerable number of adult female scale 
insects were found embedded in a band of "tree sticky" placed around 
a magnolia tree to repel the ants. This band was located 4 feet from 
the ground. The scale insects were a species of Odonaspis ^ which 
is found upon Bermuda grass close to the surface of the ground. 
There was apparently no other way for these insects to get up the 
tree except through the transporting agencies of the ants. 

On sugar cane the ants have frequently been seen carrymg around 
small sugar-cane mealy-bugs. They do not appear to pick them up 
unless they are rudely disturbed or frightened, but the fact remains 
that they have been seen transporting them. Experiments made by 
the junior author showed that the ants would pay no attention to the 
larval mealy-bugs until after the latter had commenced to feed on the 
canes and produce exudations. The following three paragraphs are 
quoted from our notes: 

Placed a piece of paper on which were about 2,000 "seed mealy-bugs" across a 
strong ant trail, and weighted it down flat, so that the ants could not get underneath 
it. At first the ants were bewildered at losing theii- trail, and ran over the paper in 
all directions. They absolutely refused to notice the young mealy-bugs, and after a 
while reestablished their trail across the paper, and commenced traveling the same 
as before. The mealy-bugs were swarming directly across the trail, bat the ants paid 
no attention to them. 

This seems to indicate that the ants have no dealings with the mealy-bugs until 
they begin to secrete the juices from the cane stalks. These young mealy-bugs had 
never fed, being taken directly from the tube in which they were hatched. Thus 
they would probably not have excreted any liquid. At the same time the ants did 
not show any hostility toward them. 

The eggs are out of reach of the ants when they are enveloped in the egg mass, as 
the waxy covering appears to entangle the feet of the ants, being slightly sticky and 
adhesive. The egg stage and young larval stages are therefore removed from the 
sphere of the ants' influence. 

Even though the actual transportation of plant lice, aphides, and 
mealy-bugs by the ants may not assume much economic importance, 
there is, nevertheless, no doubt that the ants assist these insects 
greatly m other ways. They build shelters over them, these consist- 
ing of fuie particles of earth, protectmg them from storms and hm- 
dering the attacks of parasites. These shelters have been noticed 
in many different localities. In Bulletin 52, Bureau of Entomology, 
Mr. E. S. G. Titus gives an illustration of a large shed buUt by the ants 
over the surface of a persimmon, protecting a number of Florida wax 
scales {Ceroplastes Jloridensis Comst.). These sheds are also present 

1 Determined by Mr. E. R. Sasscer. 



64 THE ARGENTINE ANT. 

in great numbers on sugar cane, Jolmson grass, willows, and oaks, 
and, in fact, in all places where a number of coccids or plant lice are 
exposed to the weather. 

The stimulation resulting from the attentions of the ants whUe 
collecting the sweet liquids appears to have the effect of greatly 
encouraging the numerical increase of the aphidids and coccids. 
During the summer of 1910 the junior author reared several genera- 
tions of sugar-cane mealy-bugs on sugar cane planted in large pots. 
One-half of these pots were isolated from the Argentine ants, while 
to the others they were allowed free access. The mealy-bugs grew 
and multiplied in both lots of cane, but there was great difference 
between the thriftiness of the isolated and nonisolated msects. In the 
pots to which the ants had access the mealy-bugs multiplied so freely 
that finally they almost smothered out the sugar cane with their 
cottony egg masses. In the isolated pots, while the mealy-bugs 
increased in numbers, they were not nearly so numerous or healthy 
looking as in the ant-infested pots. At the end of two months the 
number of mealy-bugs in the ant-infested pots probably exceeded 
the number of mealy-bugs in the isolated pots to the extent of at 
least five to one. 

That the same conditions exist in the cane fields is sho"WTi by the 
number of mealy-bugs which can be found m the fields infested by 
the Argentine ant as compared to their scarcity in fields not infested 
by the ant. Only one field under the latter conditions has been dis- 
covered as yet, but it has been watched closely for two years. The 
mealy-bugs have never become sufficiently numerous to attract the 
attention of the working hands, and they can be found only with 
considerable difficulty. On the other hand, in the fields where the 
mealy-bugs and ants are associated the former have become so 
numerous that the white cottony egg masses can be easily observed 
from the road while drivmg through the fields. 

The same thing holds true with scale msects generally. In the 
orange groves invasion by the ants is followed by a rapid increase of 
scale insects, particularly the chaff scale {Parlatoria pergandii Comst.) 
and various species of Leeanium. So rapidly do these scales increase 
that, unless prompt measures are taken against the ants, the second 
year of mfestation shows a severe curtailment of the crop, and the 
fourth or fifth year witnesses the death of many of the trees. The 
rapid decline of orange trees under conditions of heavy ant infestation 
is well illustrated by Plate VI, which shows a tree after exposure to 
attacks of the ants and chaff scales for three seasons. 

The ants constantly attend the citrus white fly (Aleyrodes citri 
R. & H.), and a marked increase in this injurious pest always accom- 
panies ant infestation. 



Bui. 122, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate VI. 




Orange Tree After Exposure to Argentine Ants for Three Seasons. (Original.) 



RELATIONS WITH OTHER ARTHROPODA. 65 

During a period of 18 months 48 species of scale insects have been 
collected in Audubon Park, New Orleans, all of which are attended 
by the Argentine ant. Many of these species, however, are visited 
sparingly, and are evidently regarded as sources of food when the 
more popular species fail to furnish a sufficient amount for the needs 
of the ants. A few species are particularly favored by the ants, and 
the trees and plants upon which they occur are always crowded with 
large numbers of the workers. 

Among these favored species may be mentioned the Magnolia scale 
(Neolecanium comuparvum Thro), which is found upon the various 
magnolia trees. This scale is very large and unarmored, and the 
young scales appear in great numbers during February and March. 
As this is the period during which the ants have the greatest difficulty 
in securing sufficient food it naturally follows that they concentrate 
upon the magnolia trees in immense numbers, and the soil at the 
bases of the trees is turned into gigantic ant nests. During June and 
July this scale is brought under control by the larva of a small black 
ladybeetle, and the number of ants in the magnolia trees falls off 
greatly. By this time, however, an abundance of scale insects and 
plant lice of many different species can be found everywhere, and the 
ants do not have to place such dependence upon the magnolia scale. 

Another species which attracts great numbers of workers is the soft 
scale {Coccus Ties'peridum L.). This species has been collected upon 
a variety of plants in Audubon Park, among which may be mentioned 
the orange, banana. Camellia ja'ponica, coral tree, cocoa tree, rubber 
trees, myrtle, and maidenhair ferns. This scale can be found in all 
stages at almost any time of the year, and is always heavily attended 
by ants. 

Other important scale insects from the Argentine ant's point of 
view are the sugar-cane mealy-bug (Pseudococcus calceolarise Mask.), 
the two barnacle scales (Ceroplastes cirripediformis Comst. and 
C.floridensis Comst.) , and the black scale (Saissetia olese Bern.) . The 
last three species are found upon a variety of plants. 

A complete list of the scale insects and aphides which this ant 
attends would comprise a check list of these species for the entire 
ant-infested territory. The following list, however, mcludes the 
more important species upon various plants and crops which are the 
most eagerly sought after by the ants. Most of the determinations 
have been made at Washington, D. C, through the courtesy of 
Messrs. E. R. Sasscer, J. G. Sanders, and Theo. Pergande. So far as 
possible the species most attractive to the ants have been placed 
nearest the host plants, and they follow m order of preference within 
certain limits. 

75508"— Bull. 122—13 5 



66 THE ARGENTINE ANT. 

LIST OF COCCID/E AND APHIDID/E ATTENDED BY THE ARGENTINE ANT. 

Upon l)amboos: Asterolecanium hamhusx Bdv., Odonaspis secreta Ckll., Odonaspis 

inusitata Green. 
Upon banana: Coccus hesperidum L., Chrysomphalus aonidum L. 
Upon cotton: Aphis gossypii Glov. 

Upon com: Undetermined aphis (probably Aphis inaidls Fitch). 
Upon figs: Pseudococcus citri Risso, Lecaniodiaspis sp., Aspidiotus camellise, Sign. 
Upon hickory, elm, hackberry, and various shade trees: Pseudococcus sp., Ceroplastes 

drripediformis Comst., Ceroplastes floridensis Comst., Chionaspis longilobn Cooley, 

Chionaspis americana Johnson. 
Upon magnolias: Neolecanium cornuparvum Thro, Aspidiotus camellise Sign., Toumey- 

ella turgida Ckll. 
Upon mulberries: Chrysomphalus tenebricosiLs Comst. 
Upon oaks: Kermes galliformis Riley. Eulecanium caryx Fitch, Eulecanium quer- 

cifex Fitch, various aphidids. 
Upon orange: Coccus hesperidum L., Parlatoria pergandii Comst., Lepidosaphes heckii 

Newm., Lepidosaphes gloverii Pack., Chrysomphalus aonidum L., Aphis gossypii 

Glov.; also the white fly, Aleyrodes citri R. & H. 
Upon palms and other ornamentals: Coccus hesperidum L., Eucalymnatus tessellatus 

Sign., Aspidiotus latanise Sign., Aspidiotus hederx Vail., Chrysomphalus dictyospermi 

Morg. 
Upon peach, pear, and other fruits: Aspidiotus perniciosus Comst., Aulacaspis penta- 

gona Targ., various aphidids. 
Upon persimmons: Ceroplastes drripediformis Comst., Eulecanium corni Bouche, Pulvi- 

naria vitis L. 
Upon strawberry: Aphis forhesi'S^ eed. 

Upon sugar cane: Pseudococcus calceolaria'. Mask., Aphis gossypii Glov. 
Upon sweet giuu : Cryptophi/Uaspis liquidambaris Kotinsky . 
Upon various shrubs: Coccus hesperidum L., Saissetia olese Bern., Pulvinaria cupanix 

Ckll., Aspidiotus latanix Sign., Chrysomphalus aonidum L. 
Upon willows: Eulecanium nigrofasciatum Perg., Pseudococcus sp. (nearci7n), Chion- 
aspis salicis-nigrx Walsh, Aspidiotus perniciosus Comst., various undetermined 

aphidids. 

In considering the remarkable increase in scale insects and aphidids 
which invariably accompanies heavy infestation by this ant one can 
not avoid taking into account the persistence with which the ants 
drive away ladybird beetles which attempt to prey upon the msects 
fostered by the ants. So thorouglily are the Coccidse and Aphididae 
protected in this manner that it is rare that a ladybird can be found 
at all on the mfested trees. The only exceptions to this rule thus 
far noted are a species of Pentilia, a few specimens of which the 
senior author found in an infested orange grove below New Orleans, 
and the coccinellid mentioned before as preying upon the magnolia 
scale. 

ANTAGONISM TOWARD OTHER INSECTS. 

The Argentine ant is strongly antagonistic to nearly all forms of 
insect life, with the exception of the Coccidae and Aphididse. The 
amount of damage it is able to inflict upon other msects, however, is 
governed by the strength, fleetness, structure, or habits of the 



RELATIONS WITH OTHER ARTHROPODA. 67 

insect attacked. Thus it is able to destroy house flies, butterflies, 
mosquitoes, etc., only when the latter are hurt or disabled, as 
under ordmary conditions they are much too swift for the ants to 
catch. In the same manner nearly all forms of beetles are strong 
enough to escape from the ants when caught, and their external 
covermg is so hard that the ants can make no impression upon it; 
but an injured beetle of any kind is very quickly overcome by the 
numbers of the ants, and his body is finally cleaned out of the shell 
piecemeal. Newly emerged adult beetles of many species are often 
captured by the ants before their chitmous integument has hardened, 
and they are then an easy prey. 

Cutworms and hairless caterpillars found upon the surface of the 
ground are destroyed in great numbers; but the ants will not burrow 
mto the ground after hidden cutworms, and most hairy caterpillars 
appear to be invulnerable to them. Web-spinning caterpillars are 
also safe from their attacks, and the spiny, mealy projections sur- 
rounding coccinellid or ladybeetle larvae appear to protect these 
latter veiy effectively. Insects and other small related animals which 
the ants can meet upon even terms are, however, almost always over- 
come; not so much on account of the individual valor of the Argen- 
tine ants as by reason of their overpowering numbers. 

Nests of the social wasps, Polistes sp., which were brought into our 
laboratory as food supplies for cultures of Pediculoides, were quickly 
found by foraging workers, and the latter soon killed and removed 
all of the wasp larvae and pupae that could be reached. Many of the 
cells in the comb of Polistes were enth-ely or partially open so that 
the ants had ready access to the insects inside. As the prey in this 
case was too large to be handled by individual ants, as many as two 
or three dozen would unite in removing a single wasp pupa or larva. 
Even the adult wasps, just emerging from the cells, were set upon by 
the ants before they had attained sufficient strength to escape by 
flight. More and more of the ants would get on these adult wasps 
until the latter were helpless and were dragged away, still alive, by 
scores of the worker ants. So anxious were the ants to get at these 
wasps that when the latter were placed on top of a fruit jar standing 
in a tray of water the ants swam the 3 inches of fresh water, climbed 
the glass sides of the jar, and contmued their attacks as before; nor 
could they be made to desist until oil of sassafras was placed upon 
the water. 

The nests of mud-dauber wasps, Pelopceus sp., were also brought 
into the laboratory for the same use as the Polistes. The mud- 
dauber larvae were of course inaccessible to the ants, but parasitic 
flies ^ which emerged from these were seized by the ants as fast as 

1 Identified by Mr. C. H. Tyler Townsend as a species of Pachyophthalmus. 



68 THE ARGENTINE ANT. 

they emerged and were summarily disposed of in the same manner 
as were the Pohstes. Invariably the flies were seized before enough 
time had elapsed for their wings to expand and diy, and only a very 
small percentage of them escaped the ants. 

Cockroaches are esteemed a great delicacy by these ants, and while 
the workers are not able to capture unmjured roaches, they attack 
in great numbers any roach so unlucky as to be injured. Dead cock- 
roaches are also eagerly visited by the ants and all soft parts removed. 
It seems almost retribution that one of the few natural enemies of the 
Argentine ant should itself be a larval cockroach (Thyrsocera cincta 
Burm.), mention of which is made on a following page. 

THE ARGENTINE ANT AND THE BOLL WEEVIL. 

Prior to the advent of the boll weevil in the territory infested by the 
Argentine ant there was considerable speculation as to whether so 
combative an ant might not prove to be an insect of some value in 
protecting the cotton crop against weevil ravages. Any hopes of this 
kind which were entertained have not thus far been realized. In one 
rather ununportant respect the ants seem to annoy the boll weevils. 
At Baton Rouge the Louisiana Experiment Station had afewsmall plats 
of cotton, aggregating less than an acre, within the city limits and in a 
section where the Argentme ants were exceedingly abundant. The 
plats were bordered on one side by the Louisiana State University 
campus, with its large oak trees sheltering hundreds of ant colonies, 
and on the other side by the batture of the Mississippi River, which 
was likewise a seething mass of ant colonies. The ground in the cotton 
plats was therefore heavily infested by the ants, and when this field 
also became infested by the boll weevil the outcome was watched with 
considerable hiterest. During September, 1909, it was found that 
the ants, in their steady patrol of the plants while attendmg cotton 
lice, worried the adult boll weevils considerably. Whenever an ant 
encountered a boll weevil it would nip the legs of the latter, usually 
causing the weevil to fly to another plant or drop to the ground. In 
no case were the ants found killing fully matured weevils, though in a 
few instances they did attack and kill unhardened weevils which had 
just issued from infested squares. The great abundance of ants in 
these plats evidently resulted in many of the weevils being driven off, 
for something of a top crop was produced in the fall of 1909. It is 
worthy of note in this connection that the heavy ant infestation 
obtaining in these plats will not be duplicated in large cotton fields 
for many years to come, if, indeed, such will ever be the case. Condi- 
tions in large cotton areas are not such as to attract the Argentine ant 
in numbers. It was also of interest to note that the presence of the 
ants in these particular plats resulted in an abnormally heavy infesta- 



KELATIONS WITH OTHER ARTHROPODA. 69 

tion of the plants by the '' cotton louse," Aphis gossypii Glov., 
throughout the entu-e growing season. 

Were the jaws of the Argentme ant powerful enough to pierce the 
cotton squares so that they could remove the boll-weevil larvse, and 
were they so inclined, they might be of substantial service in destroy- 
ing this pest. However, repeated experiments made by the sjenior 
author proved conclusively that the ants would not do this. The 
following experiment will serve as an illustration of those carried out: 

On July 10, 1908, three weevil-infested squares were placed on the 
food table of an Argentine-ant colony in the insectary at Baton Rouge. 
The workers crawled over them constantly for three liours, but made 
no attempt to bite into them and evidently did not suspect the pres- 
ence of food inside of them. Afterwards the weevil larvae were re- 
moved from the squares and placed, alive and uninjured, on the food 
table. The ants attacked them, hesitatingly at fii'st and then with 
avidity, and in the course of a minute one large weevil larva was 
dragged an inch across the food table, vertically another inch, and 
into the vestibule of the nest. Another lot of weevil-infested squares 
was placed on a board inside the insectary where the ants had been 
securing other food for several days. The squares were left here for 
five hours, during which time tlie ants crawled over them constantly, 
but made no effort to open them. The ends of the squares were then 
broken off so that the ants could enter them if they chose. None 
entered. Presently some of the weevil larvae wriggled themselves 
completely out of the squares and they were then attacked by the ants 
and dragged away. 

These and sunilar experiments lead one to the conclusion that the 
Argentine ant will never be of material value as an enemy of tlie boll 
weevil. In fact, in this respect it can not hope to approach in effi- 
ciency tli»e common native fire ant, Solenopsis gcminata Fab. 

BENEFICIAL ASPECTS OP THE ANT's ACTIVITIES. 

In some few cases tlie predatory habits of the ant take on a bene- 
ficial aspect. In the summer of 1908 Mr. R. C. Treherne was associ- 
ated with us in the investigation of the sorghum midge (Diplosis) 
Contarinia sorgJiicola Coq. In the course of his work Mr. Treherne 
placed heads of sorghum, milo maize, etc., in cages for the purpose of 
rearing the adult midges. In a very short time he found that the 
Argentine ants were invading the cages and were carrying away the 
adult midges almost as fast as they emerged. (See fig. 10, from draw- 
ing by Mr. Treherne.) To continue the observations it was necessary 
to isolate the cages over trays of water or oil. For the purpose of 
more closely observing the capture of the midges by the ants, about 
200 of the former were placed inside a large glass bell jar. The jar was 
raised a trifle at its lower edge by the insertion of a match. In the 



70 



THE ARGENTINE ANT. 



course of three minutes two Argentine workers had found their way 
into the jar and each had captured an adult midge. Other workers 
soon followed. In about 15 minutes fully three-fourths of the flies 
had been captured and at the end of 30 minutes all had been either 
captured and carried away or were in possession of workers. The 
first midges captured were quickly carried to the ants' nest, but pres- 
ently the workers seemed less appreciative of their prizes and spent 
much more time in playing with them, although in but few cases were 
the midges relinquished. Occasionally a midge would succeed in 
taking flight after a worker had taken hold of it; in such cases worker 
and midge tumbled to the floor, but without the midge being released. 
That the workers were unable to see the midges was made evident 

many times over in this experi- 
ment, for workers repeatedly passed 
within one-sixteenth of an inch of 
their prey without even changing 
the direction of travel. Only when 
the worker touched the midge with 
her antennae could she locate the 
latter. 

Later on it was found that the 
ants thoroughly patrolled the sor- 
ghum heads in the field and not only 
captured the midges as they were 
emerging from their pupal cases be- 
tween the glumes but also removed 
the pupae themselves. That this 
ant is by far the most important 
natural enemy of the sorghum midge 
in southern I^ouisiana there can be 

FIG. lO.-Argentine ant removing the pupa of a HO doubt,^ but itS SCrvicCS in tllis 
sorghum midge from between the glumes of a regard do not begin to CXpiate itS 
sorghum head. (Orlgmal.) .^ 

many other crmies. 
The Argentine ant is a persistent enemy of the white ants, or 
termites, and will capture and kill them at every opportunity. Espe- 
cially durmg the mating season of the termites every male and queen 
that falls to earth is quickly set upon by the ants. The latter cut 
off their wmgs, and frequently also legs and antennae, and then bear 
them away, still alive, to theu- nests. Wherever colonies of termites 
are accidentally exposed the ants soon destroy them, carrying away 
all stages. Not infrequently one finds the Argentme ant colonies 
domiciled in the old termite galleries in logs and timbers, the assump- 
tion being that the ants had first destroyed the termite colonies and 
then taken possession of their domiciles. When winged termites were 

' Dean, Harper, Bui. 85, Part IV, rev., Bur. Ent., U. S. Dept. Agr., p. 57, lon. 




EELATIONS WITH OTHER ARTHROPODA. 71 

furnished to the ants in our artificial formicaries the wings were 
quickly amputated, although the termite itself was not always carried 
into the formicary, possibly because, in such cases, the ants were 
already bountifully supplied with animal food. 

The Rev. Albert Biever, of New Orleans, whose observations on 
the Argentine ant are elsewhere mentioned, is authority for the 
statement that these ants have in many cases entirely exterminated 
the bedbugs in the houses of many of the poorer people in New 
Orleans. 

Father Biever also states that in some sections of the city the 
''red bug," or cliigger, has entirely disappeared with the advent of 
the ants. The junior author's observations in Audubon Park, New 
Orleans, are of similar nature, the chiggers being entirely absent 
where once they were a plague. At the same time the senior author 
ctill retains some very unpleasant memories of daily attacks by 
chiggers on premises in Baton Rouge which were heavily infested 
by the ants. We are thus unable, as yet, to state with certainty 
that the ants always destroy these annoying pests. 

The attitude of the Argentine ant toward other species of ants has 
already been discussed and its action in destroying other ants takes 
on either a beneficial or injurious aspect according to whether the 
annihilated ant is itself one of beneficial or injurious nature. 

SYMBIOTIC RELATIONS. 

The relationships which exist between the Argentine ant and those 
insects or other creatures which it tolerates in its nests or in the 
near vicinity can not be considered as symbiosis, yet mention of these 
may be permissible at this point. Despite the hostihty which these 
ants exhibit toward most insects which are not directly of service 
to them, a few instances have been noted in wliich other insects and 
crustaceans were permitted to live in close proximity to their nests, 
or even within the nests themselves. 

Certain staphyhnid beetles have frequently been found in decayed 
logs wliich were full of Argentine ants. Efforts have been made to 
keep some of these beetles in the artificial formicaries along with 
colonies of the ant under observation, but the results have been 
variable. In expermients of this kind made by the junior author 
the beetles were invariably set upon by the ants in the formicary 
and either killed or driven out. In similar experiments by the 
senior author no apparent attention was paid to the beetles, so far 
as could be observed, and they were tolerated in the formicary for a 
week or longer, after which they evidently left of their own accord. 

On August 17, 1909, a large ant nest was discovered in Baton 
Rouge under a large dry-goods box. About 20 specimens of ''spittle 



72 THE AKGENTINE ANT. 

insects" (family Cercopidae) were also present in the same nest, 
attached to straws of grass. These were apparently protected from 
the ants by the wet, sticky secretion which surrounded them. This 
is the only instance, however, in which the presence of these insects 
has been recorded in the colonies. 

Sowbugs (Oniscidffi) apparently go among the Argentine ants with 
impunity. These little crustaceans are often found in the ant 
nest, especially if they are located under boards or boxes in moist 
places. There does not appear to be any relationship existing, and 
the ants are apparently indifferent to their presence. 

With the exception of two species of mites, which are true inquHines 
in the ant colonies, the Argentine ant does not pay much attention 
to the majority of mites and spiders. Mention is made on a later 
page of certain spiders which prey upon the ants to a limited extent. 
The cattle tick (Margaropus annulatus Say) flourishes with, undi- 
minished vigor in the ant-infested region, and the same may be said 
of the ''red mite" of the orange and the red spider of ornamental 
plants (Tetranychus himaculatus Harv.). 

INQUILINES. 

Only two true inquilines, both mites, have thus far been found in 
the colonies of the Argentine ant. These were first discovered at 
Baton Rouge by the senior author in 1908, and were subsequently 
found in various localities and in nests of various kinds, usually in 
those located in masses of decaying vegetation or litter^ Soon after 
they were first found specimens were sent to Dr. L. O. Howard, who 
submitted them to Mr. Nathan Banks, of the Bureau of Entomology. 
Mr. Banks found them to be new, and his descriptions of them were 
published in the Journal of Economic Entomology, volume 1, pages 
263 and 264 (19.08), together with notes on their habits, by the senior 
author, 

NATURAL CONTROL. 

As compared with most injurious insects which reach great abun- 
dance the Argentine ant is remarkably free from natural enemies, 
and very few of these have been noted during the course of our inves- 
tigations, while even these few are of little importance. No true 
parasites of this ant have been observed, and apparently the only 
enemies are predatory ones. 

NATURAL ENEMIES. 

INSECTS AND SPIDERS. 

In 1909 Mr. Harper Dean observed a small cockroach capturing 
Argentine ant workers m a room in Baton Rouge, La. This insect 
from time to time caught up and ate workers which were traveling 



NATURAL CONTROL. 73 

about the floor. The cockroach was captured and sent to the Bureau 
of Entomology, where it was identified by Mr. A. N. Caudell as a 
nymph of Thyrsocera cincta Burm., a species occurring in the south- 
ern United States, Mexico, and Central America. A sunilar habit by 
individuals of this species was subsequently observed by the senior 
author on one or two occasions, but the number of ants destroyed 
by this insect is certamly inappreciable. 

A jumpmg spider of the family Attidiie was seen to capture a few 
workers, and various species of the cobweb weavers (Theridiidae) had 
the habit of reposing beneath the stands supporting our artificial 
formicaries and there depleting the colonies under observation. In 
fact, so persistent were they that it was necessary to, examine the 
stands daily and destroy these spiders. Among the most abundant of 
these was one which was identified by the late Prof. B. H. Guilbeau, of 
the Louisiana State University, as Theridium tepidariorum. Spiders 
of this family were not observed destroying ants in outdoor colonies, 
but it is possible that they do so. 



On one occasion Mr. G. A. Runner observed an English sparrow 
industriously picking up the Ai-gentine workers from a trail which 
crossed a wide roadway at Baton Rouge. This habit is not, how- 
ever, a common one with this bird. 

The flicker or yellowhammer, Colaptes auratus, has often been seen 
industriously digging up shallow ant nests in lawns and grass plats, 
evidently for the purpose of obtaming the pupte and larvae, and 
should doubtless be credited with bemg the most important natural 
enemy which this ant has in the South. Our knowledge of the extent 
to which native birds subsist upon these ants is very limited as yet, 
and the subject is one well worth more complete investigation than 
we have been able to give it. 

EXPERIMENTS WITH PEDICULOIDES. 

The idea of finding some parasite which would destroy the ants 
naturally suggested itself early in our investigations. Owing to the 
readiness with which the small parasitic mite, Pediculoides ventricosus 
Newp., parasitizes the larvae of wasps and beetles whenever it can 
obtain access to them it was thought worth while to see if this para- 
site could be successfully used against the ant. For our experiments 
we first reared enormous colonies of these mites on living wasp larvae 
and thereafter placed these infested larvae in the formicaries, where 
they could be closely observed. The folloA\'ing experiment will illus- 
trate the results obtained : 

For the experiment we selected a large populous ant colony which 
was domiciled in a plaster of Paris Janet cage of several chambers. 



74 THE AROENTINE ANf. 

All immature stages of the ant were present in abundance. On March 
14 the cover to one of the living chambers was raised and one of the 
mite-iiifested larvae was dropped in among the workers and larvae in 
the formicary. The workers set to work immediately to kill the 
hundreds of mites. The larval mites were picked up in the w^orkers' 
mandibles, chewed a bit and then thrown aside. Adult mites were 
seized by the legs and vigorously pulled until they released their liold 
on the wasp larvae, after which the workers would crush them in their 
mandibles. However, the subsequent developments were entirely 
unexpected. A worker was seen to mount the wasp larva, eagerly 
destroying mites and becoming at the same time covered with a dozen 
or more of the mite larvae. Within a minute the worker desisted 
from destruction of the mites about her and turned her attention to 
the ones on her body, trying to dislodge them by rubbing head and 
abdomen with lier legs. Failing thus to get rid of them, she resorted 
to various gymnastic performances, such as jumping and rolling over. 
Soon afterwards her movements became slow and feeble and finally 
ceased entirely, it being evident that she had either been killed or 
paralyzed by the bites of the larval mites. Observations were sus- 
pended until March 18, when it was found that the adults and larvae 
of Pediculoides were greatly reduced in numbers. No mites could be 
seen on any of the ant larvae or pupse, and all of the latter had been 
removed from the chamber where the mites were introduced. 

The workers m leaving the cage to forage were compelled to pass 
through the infested chamber, but m doing so they made the widest 
possible detour about the mite-infested material. This status of 
affairs continued for some time, the mites gradually decreasing in 
numbers until by April 28 they had all disappeared. On this date 
cultures of the mite were again introduced into the colony, but in 
much greater quantities than before. A spoonful of mite-infested 
wasp larvae was placed in each chamber of the formicary. The ants 
did not this time attempt to kill the mites, but inside of two minutes 
after the introduction of the latter the colony had completely deserted 
the formicary, takmg with it all eggs, larvae, and pupae. Not being 
able to find other suitable quarters on account of the water surround- 
ing the formicary, the ants on the following day decided to return to 
the nest. They attempted to remove the Pediculoides, but the mor- 
tality among the workers was heavy, many being carried out at the 
entrance. On the follow^ing day the number of dead workers was too 
great for removal, and many of them remained in the cage. The con- 
tinual warfare against the mites continued for several days, the ant 
colony becoming by May 6 severely depleted in workers as well as 
in larvae, some of which were killed by the mites. At the same time 
it was evident that the Pediculoides were bemg destroyed much more 
rapidly than they could increase. After May 6 the ant colony ap- 



NATURAL CONTROr.. 70 

peared to recover slowly. By July 22 the colony had completely 
resumed its normal condition and the mites had been exterminated. 
That the Pediculoides could live and breed upon the ant larv^ was 
established by placing the latter in a glass dish which was isolated 
from all workers and permitting them to become infested. On them 
the Pediculoides grew and increased as well, apparently, as on wasp 
and other larvae. Such enormous cultures of the mite as were intro- 
duced into the ant colonies in these experiments could not possibly 
occur in nature, and it seems a safe conclusion that this parasite can 
make no headway against the ant under normal conditions. 

EXPERIMENTS WITH FUNGOUS DISEASES. 

During 1909, at Baton Rouge, several experiments were made in 
the attempt to inoculate the ants and their larvae with the chinch-bug 
fungus, Sporotrichum glohuliferum . Cultures were prepared from 
beef extract and corn meal, sterilized at a pressure of 18 pounds per 
square inch for 30 minutes at a temperature of 256° F,, and these 
were then inoculated with the fungus from a dead beetle. After these 
cultures had been stored for about a week in a dark, damp place, 
they all showed a heavy white layer of fungous growth over the sur- 
face, and this layer was used in the experiments. 

Large quantities of this fungus were placed in Janet cages which 
contained strong and healthy colonies of ants with many immature 
stages. For a short time the workers would busy themselves carry- 
ing out the fungus and dropping it over the side of the cage support, 
but after a time they apparently became accustomed to its presence. 
It grew and increased inside the-apartments in which the ants and their 
young stages were domiciled until it formed a heavy white mass over 
nearly everything, but m not a single instance was an ant or a young 
stage observed which appeared to be in the least inconvenienced by it. 

As a number of dead ants were found covered with fungi the 
various organisms on them were isolated and cultures made. The 
principal fungi obtained were Aspergillus and Penicillium. Cul- 
tures of these were also introduced mto the ant colonies, but without 
effect. It was therefore concluded that they were purely sapro- 
phytic on the dead ants on which they were found. 

Attempts were also made to infect colonies with Bacillus larvse, 
the germ causing the disease among honey bees known as American 
foul brood. Owing to the fact that this bacillus attacks the larval 
stages of the honey bee, and considermg the similarity of ant and bee 
larvae, it was thought that this disease might attack the larval stages 
of the ant. The experiments were made in a locality where the ant 
infestation was very heavy but where honey bees were not kept. 
Honey was thoroughly mixed with broken and mashed brood combs 
containing bee larvae badly infected with foul brood, and this honey 



76 THE ARGENTINE ANT. 

was then fed iii abundance to foraging workers. Subsequent exami- 
nation of the colonies receiving this infected material failed to show 
any indication of the disease. 

No attempt w^as made to experiment with this disease under labora- 
tory conditions, on account of the danger of accidentally infecting 
honey bees in the neighborhood. 

LOW TEMPERATURES. 

The winter temperatures experienced at Baton Rouge, La., seemed 
not to produce any appreciable mortaUty among the ants. During 
the winter of 1909-10 a colony at Baton Rouge was kept out of doors 
all winter with no other, protection than the plaster of Paris walls of 
the cage in which it was confined. This colony successfully with- 
stood a temperatm-e of 22° F., the lowest temperature recorded 
during the winter. It is safe to assume that in their underground 
nests and in well-protected situations they can withstand a much 
lower degree of cold than this. 

FLOODS. 

Heavy rains appear to be the only meteorological jjhenomena 
which produce any appreciable effect upon the Ai^gentine ants, but 
even in this connection it is worthy of note that the most heavily 
infested sections at present are within regions of exceedingly hea^^ 
annual rainfall. 

After sudden severe rainstorms it was noticed that the ditches and 
drains at Baton Rouge and New Orleans contained thousands of the 
dead ants, evidently washed from trees and ground before they could 
reach a place of safety. The sudden rising of flood waters over low- 
lands would appear to destroy many colonies and the larvae in them, 
yet, strange to say, the batture along the Mississippi River, wliich is 
annually covered for several weeks with several feet of water, con- 
tinues to be an area of approximately maximum infestation. So 
facile are the ants in migrating to higher grounds or in ascending 
trees, taking \vT.th them all larvae and pupae, that it is hkely that the 
mortality from this source is much less than would be expected. 
The mere destruction of foraging workers by rains does not effect any 
appreciable duninution in the rate of increase since, if the colonies 
themselves remain unharmed, the deposition of eggs and the rearing 
of more workers continues unabated. 

METHODS OF REPRESSION. 

It is as a household pest that the Argentine ant has forced itself 
most into prominence, particularly in the infested cities and towns, 
although it is doubtful if the financial loss due to its inroads in this 



METHODS OF REPRESSION. Y7 

respect even begins to compare with the losses suffered by the florists, 
bee keepers, and orange growers. Early in the course of our studies 
we undertook experiments looking to the development of measures 
by which householders could obtain some relief from this pest. 

A successful campaign against the Argentine ant is by no means 
devoid of work, but the control measures thus far devised are no 
more cumbersome or expensive than those employed in the warfare 
against many other insects, and their intelligent employment is found 
well worth the while in reduced annoyance from tliis pest. 

Studies of the ant's life liistory early developed the fact that per- 
manent relief can be obtained only by actual destruction of the ants 
themselves. The use of repellents only serves to permit the contin- 
ued increase of the pests and to postpone the time when more laborious 
methods of warfare must be adopted. Not only is it necessary to 
kiU the ants outright, but it is also necessary to adopt means which 
will kill the queens. It is hardly necessary to call attention to the 
difference between killing ants and the usual insects with which we 
have to contend. If one kills a female gipsy moth or boll weevil, for 
example, possible future progeny of that particular individual is made 
mipossible. Such is not the case when one destroys a worker ant, 
for the rate of increase and the development of future generations are 
in no way interfered with. This is true for the reason that the workers 
take no part in reproduction, aU eggs being deposited by the queens. 
That the destruction of foraging workers does not materially affect 
the domestic economy of the colony or retard the rate of increase by 
reducing the available food supply is shown by repeated observations 
upon the nmnber of foragers required to keep the colony supphed with 
food. In the artificial formicaries counts were made of the number 
of workers going out for food during periods varying from five hours 
to several days, and in no case did the number of foraging workers 
out at one tmie exceed more than 1 per cent of the number of indi- 
viduals in the colony. From this we naturally conclude that less than 
1 per cent of the workers can keep the remainder, including the queens 
and immature stages, supplied with food. These observations were 
made in cases where the food supply was only a few inches from the 
nest and was always in abundance. In times of food scarcity, and 
when it is necessary for the workers to travel considerable distances in 
order to reach a food supply, a larger percentage would have to engage 
in foraging. Observations by the junior author upon a large number 
of field colonies leads him to the conclusion that even under the most 
adverse conditions not more than 10 per cent of the workers are 
required for foraging. Under normal outdoor conditions the food 
supply is abundant and at such times it is very doubtful whether more 
than 2 per cent of the workers are ever engaged in foraging at any one 
time. The futihty of destroying the foraging workers is therefore 



78 THE AEGENTINE ANT. 

self-evident, for the number of workers leaving a colony during any- 
given period is little if any greater than the number reaching maturity 
within the colony during the same period. 

In spite of these facts repellents are very desirable and their use is, 
under most conditions, absolutely imperative in the protection of 
foodstuffs, such as sugars, candies, cakes, molasses, honey, vegetable 
oils, fresh meats, etc. 

EXPERIMENTS WITH REPELLENTS. 

Our first experiments consisted in testing the various substances 
which had been used in successfully repeUing other species of ants. 

Experience "with artificial formicaries and with the hives of honey 
bees very quickly showed that water would deter the workers for only 
a short time. In our first experiments with colonies kept under 
observation the nests were placed on platforms supported above trays 
of water. As soon as the water had stood for a few hours minute 
dust particles, settling from the air, formed a very thin, almost imper- 
ceptible scum on it, and this the workers traversed with ease. A 
scum which, when \dewed by reflected light, is barely perceptible to 
the eye will support the workers. When such standing water was 
removed and fresh substituted for it the ants would plunge into it as 
before, evidently expecting the scum to be there stiU. Instead of 
drowning, as might be expected, the workers merely swam, or crawled 
upon the bottom of the tray until they reached the edge or the wooden 
support of the nest, when they proceeded to crawl out. Workers 
thrown into water can readily crawl up one's finger or up a stick if it 
is brought near them. The senior author has observed workers 
which had accidentally fallen into a glass decanter three-fourths full 
of water gain a foothold on the smooth glass sides and crawl out suc- 
cessfully, feet up and body down, on the wet glass. The workers wiU 
apparently not enter fresh water voluntarily, but evidence indicates 
that they will sometimes do so in the attempt to reach their nests or 
to reach some much-desired food supply. When running over a film 
of oil or dust upon the water the feet and legs do not get wet, but 
when the film breaks through, as sometimes happens, the worker 
swims with her legs and a portion of the body submerged. Running 
water, such as a stream in a ditch or trough, seems to be a successful 
repellent, but the practical uses of such a stream are very Umited. 
The use of running water as barriers to prevent the spread of infesta- 
tion in orange groves is more fully described upon a subsequent page. 

Sir John Lubbock in his book, "Ants, Bees and Wasps," describes 
bands of fur which kept the ants within his artificial formicaries. 
The kind of fur used by Sir John Lubbock is not specified, but the 
finest we were able to secure was that from an ordinary "cottontail" 
rabbit. With this the following experiment was made: 



METHODS OF EEPEESSION, Y9 

Two devices were prepared, each consisting of a small wooden box 
nailed to the top of a rounded 2-inch stake about 2 feet in length. 
Around the support (stake) of one box a roll of the fur was tightly 
placed, arranged so that the hairs projected downward and so that the 
ants would have to crawl "against" them in going up the stake. 
Fur was not placed upon the other device. The latter was stuck in 
the ground and a supply of honey placed in the box. The ants 
visited the honey at once and as fast as they removed it the supply 
was renewed. This continued for several days, when this device was 
removed and the one with the fur was put in its place, also with honey 
in the box. The interruption of the "trail" confused the ants for a 
little, but within a minute's time they were going up the new device 
and working their way persistently among the hairs of the fur. In 
a short time they were able to get through it, when they continued to 
the food supply at the top and removed it as before. The workers 
were forced to make their way slowly through the fur, wTcstling in 
turn with the hairs in their way, but at most the fur did no more than 
delay them a little; it did not repel them in the least. 

Various experiments were made with certain proprietary and coal- 
tar disinfectants for protecting food supplies from the ants. Wood- 
work rubbed or painted with these substances was not crossed by the 
workers during periods of from 2 to 48 hours after the appUcations, 
but none of these substances was effective for more than two days, 
on of citronella seemed more distasteful to the ants and they would 
not cross woodwork treated with it as long as the odor remained. 
Evaporation of this oil is, however, quite rapid. 

The use of zenoleum powder was found quite effective. Sprinkled 
heavily on the floors of infested houses it killed many of the workers 
with which it came in contact and answered fairly well for breaking 
up trails and causing the workers to seek food elsewhere. It was 
also found of some service in keeping ants out of the nests of sitting 
hens. 

Pine tar was not effective. In an attempt to feed honey to bees in 
the open air the feeder was supported on a stick around which were 
placed two separate bands of fresh pine tar. The feeder was placed 
out in the afternoon and by 6 o'clock the next morning the ants had 
crossed both bands of tar and the honey was black with them. To 
stop them, two fresh bands of tar were applied. Within 30 minutes 
the ants which were trying to get out of the feeder had forced their 
way into the tar in sufficient numbers to form a bridge and over this 
the ants were soon passing freely to and fro, despite the strong odor 
of the tar itself. 

The following experiment proved the inefficiency of tobacco dust : 
In the middle of a large iron pan with flat bottom was placed a dish 
of honey. This dish was surrounded by a layer of tobacco dust from 



80 THE ARGENTINE ANT. 

1 to 2 inches wide and thick enough to obscure entirely the bottom of 
the pan. This arrangement was made at 2 p. m., and by 5 p. m. the 
ants were crossing the tobacco dust and getting the honey with as 
much f aciUty as they would have crossed an equal amount of soft dirt. 
The experiment was repeated, finely powdered sulphur being substi- 
tuted for the tobacco. The sulphur was not crossed so quickly as the 
tobacco dust, but within 24 hours the ants were crossing it freely. 
On one occasion the senior author planted a small lettuce bed, and 
thinking to protect the seeds untU they germinated, he spread over 
the surface of the bed a layer of tobacco dust covered in turn by a 
layer of powdered sulphur. The ants got the seeds. 

Tree tanglefoot, when placed about the trunks of trees up which 
the ants were traveling, checked them for periods varying from a few 
hours to three or four da3^s. However, a more dilute form of this 
material, used with much success in the gipsy moth work in Massa- 
chusetts by ]\Ir, D. M. Rogers, has recently been tested by the junior 
author with the result that in one case it kept the ants off the trees for 
as much as two weeks without being renewed. There is therefore a 
possibility that this special form of tanglefoot may have a use in the 
protection of trees. 

Kerosene acts as a repellent until the odor has largely disappeared, 
but a fUm of kerosene on water only affords a good floor for the ants 
to travel on. 

Various devices in the form of inverted troughs of tin or other 
smooth surfaces have been tried without success. 

Crude petroleum, of all the liquids tested, has proved to be the 
most effective repellent. When placed in dishes supporting the legs 
of tables, benches, etc., it wUl continue to repel the ants even after a 
great amount of dust and trash has accumulated in it. Its use 
indoors, owing to its oily nature and disagreeable odor, is of course 
impracticable. Out of doors it is useful for giving temporary pro- 
tection to such food materials as sugars, molasses, honey, etc. 

CORROSIVE SUBLIMATE AND "ANT TAPES." 

The only repellent found to possess any merit (aside from sweetened 
arsenical solutions, described below) was dry corrosive sublimate. 
Woodwork or cloth which has been treated with a saturated water 
solution of corrosive sublimate and allowed to dry will not be crossed 
by the ants while any of the sublimate remains. This fact is utilized 
in a practical way by soaking ordinary cotton tape about 1 inch wide 
in the corrosive sublimate solution, wTinging it out, and then drying 
it. When this "ant tape" is fastened around the legs of tables, edges 
of shelves, etc., the ants will not cross it for many months, provided 
only that it is not allowed to get wet. The explanation of this re- 
markable action of the sublimate may be found in the extremely 



METHODS OF REPEESSION. 81 

irritating effect which it has on tender membranes and surfaces. 
The finely powdered subhmate and the minute crystals when inhaled 
cause a severe irritation of the throat and nostrils, giving rise to 
sneezing and nasal discharges. The continued or careless handling of 
freshly made ant tape will often have the same effect. It seems not 
improbable that the sublimate particles may have somethmg of an 
irritating effect upon the sensory organs of the ants. The ants are 
quick to detect and avoid corrosive sublimate even when it is in solu- 
tion and mixed with other substances. All attempts to poison them 
with this substance have been ineffectual, for they can not be induced 
to partake of their most favorite foods when the latter contain the 
poison in as weak a proportion as 1 to 500. 

In some of the tests made by the senior author the corrosive subli- 
mate tape has been found to retain its efficiency for over 11 months in 
rooms where, except when the temperature was too low for insect 
activity, workers could be seen at aU hours of the day and night. 

Our method of preparing the tape is first to heat corrosive sublimate 
and water in a porcelain or granite-ware vessel until the maximum 
amount is dissolved. This solution is allowed to cool to ordinary 
temperatures, filtered, and ordinary cotton or binding tape is soaked 
in it for several hours. The tape is then removed and pinned upon a 
wall to dry, after which it is ready for use. It is very important that 
no iron, tin, or steel come in contact with the solution, or with the 
tape itself after being prepared. The tape is effective for only a short 
time when used on metal surfaces. The extremely poisonous nature of 
corrosive sublimate must be continually kept in mind, both in the 
preparation of the solutions and tape and in the use of the tape itself. 
With this tape it is a comparatively easy matter so to isolate dining 
tables, kitchen cabinets, refrigerators, etc., as to protect all food 
supplies in the ordinary residence. The same method is constantly 
used by confectioners in infested sections for the protection of their 
candy cases and supplies. 

EXPERIMENTS WITH FUMIGANTS AND CONTACT INSECTICIDES. 

Following the announcement by Mr. R. S. Woglum,' of the Bureau 
of Entomology, in September, 1908, that he had succeeded in 
destroying colonies of other ants with a solution of potassium 
cyanid, considerable interest was aroused in the question as to 
whether the same method could be used with success against the 
Argentine ant. The senior author conducted a number of experi- 
ments at Baton Rouge to determine this pomt, among which the 
following illustrates the results obtained: 

1 Los Angeles Times, Los Angeles, Gal., Sept. 20, 1908. 
75508°— Bull. 122—13 ^6 



82 THE AEGEKTINE ANT. 

A solution of potassium cyanid was made at the strength of 
1 ounce of 98 per cent cyanid to 1 gallon of water. The site selected 
for the experiment was the area surrounding a few small cotton 
plants which were heavily infested with the cotton louse, ApJiis 
gossypii Glov. Around the plants the earth was literally honey- 
combed by numerous small colonies of the Argentine ant, the workers 
of which were in constant attendance upon the aphides. The 
experiment was made at 11 a. m. on a bright day, with the tempera- 
ture at about 77° F., when the workers were busily visitmg the hce 
and foraging elsewhere for food and when the activities of the colonies 
were at about a maximum. The solution was sprayed onto the 
trails of traveling ants and the ground itself was sprayed until 
thoroughly wet with the solution. By the time the spraying was 
completed the odor of the cyanid was so strong as to affect the 
operator. In spite of this the solution did not immediately kill the 
workers with which it came m contact, but they appeared to suc- 
cumb withm about five minutes after the spraying. Five hours 
after the spraying the odor of cyanid was still very strong and the 
number of dead workers on the surface of the ground fully equaled, 
or exceeded, the number of living ones in sight at the time of spraying. 
Many live workers were busily engaged in carrying away the dead. 
The ground was exammed and thousands of hving ants in all stages — 
workers, pupae, larvae, and eggs — ^were found less than half an inch 
below the surface. Two days later the area was again examined 
and the ant colonies were apparently as populous as ever. This 
and other experiments seemed to demonstrate the impracticability 
of using this solution for destruction of the colonies, particularly as 
the earth would have to be treated with a sufficient amount of the 
solution to saturate it thoroughly to a depth of several mches. This 
would probably destroy all vegetation, would be expensive, and 
would involve the risk of injury to or loss of life by the operator and 
others. For species constnictmg compact nests having single or 
few openings the solution is doubtless effective but, owing to the 
multitudmous openings and galleries of the Argentine ant nest, 
destruction could be accomplished only by the use of enormous 
quantities of the solution. 

The resistance of this species to hydrocyanic-acid gas was well 
illustrated in experiments made in attempting to fumigate the 
winter trap-boxes in orange groves. These trap-boxes are described 
more in detail on pages 95-96. They were about 2 feet wide, 2 feet 
high, and 3 feet long, made of rough lumber and filled with decaying 
cottonseed and hay. During the winter months these boxes con- 
tained enormous colonies. For fumigating them to destroy these 
colonies galvanized-iron covers were made (see Plate XII) which 
would fit over them easily. A 6-inch hole was made in the top of each 



METHODS OF EEPEESSION. 83 

cover-box for the introduction of the chemicals used in fumigating. 
Just beneath this opening, which could be closed practically air-tight, 
was placed the usual earthenware crock for holdmg sulphuric acid 
and water. Experimental fumigation of these boxes was commenced 
with a charge of I ounce of 98 per cent potassium cyanid and the 
requisite amounts of water and sulphuric acid. This strength was 
found not to kill any ants m the box except those wliich were actually 
outside the packhig at the time of fumigation. Gradually this 
charge was increased until as much as 4 ounces of cyanid were used 
at a tune m the inclosed space of 22 cubic feet. Even at this strength, 
which corresponded to 18 ounces of cyanid per 100 cubic feet, ants 
more than 8 inches from the outside of the box were not affected by a 
confuiement of four hours. In later experiments an hon rod was 
used to make holes all through the contents of the box and the same 
charge used as before, 18 ounces of cyanid per 100 cubic feet. After 
the gas had been confuied for five hours the boxes were examined 
and it was found that only those withm a couple of inches of the 
perforations were killed. Larger charges could not be used, simply 
because the cover-box would not contain a generator of sufiicient 
capacity. Even had a charge heavy enough for effective results 
been found its cost would have been prohibitive in practical field 
work. 

Experiments were accordmgly undertaken wdth bisulphid of 
carbon for destruction of the ants m the boxes. Holes were made to 
the very bottom of the contents, bisulphid poured mto these, and 
the metal cover placed over the box, its lower edges afterwards 
bemg mounded up with dirt. One-half pound of bisulphid, used in 
this manner and confuied by the metal cover-box for five hours, 
destroyed all ants, and all stages, in the boxes. Mention is made 
of the use of this fumigant on page 96. 

Other experiments made with the bisulphid of carbon showed 
it to be the most available fumigant for the destruction of colonies 
m accessible situations. 

When colonies are so situated that they can be fumigated with 
bisulphid nothing is more effective for their destruction, but the 
difficulty of applymg this measure lies in the situation of colonies 
in all sorts of inaccessible places (see list of nesting places, p. 55) 
and to the fact that m heavily infested areas the gaUeries of one 
nest are practically contmuous with those of others, affording many 
ants the opportunity of escapmg from the fumes. 

Such substances as hot water, kerosene, crude oil, etc., will, of 
course, destroy the ants sprayed with them and often it is quite 
practicable to use these substances for the destruction of colonies 
that are discovered by turning over boards, pieces of wood, piles 
of trash, etc. 



84 THE ARGENTINE ANT. 

Many preparations liave been sold throughout the infested sections 
for the purpose of destroying the ants. In nearly all cases these 
have been merely fluids which would kill the ants when coming 
in contact with them and the directions have stipulated that the ants 
should be sprayed with the solutions when on their foraging trails. 
In view of the foregoing statements relative to the small proportion 
of workers foraging at any one time it is not at aU remarkable that 
such preparations have always yielded nothing but disappointment, 
even though enormous numbers of foraging workers were destroyed 
by their use. 

EXPERIMENTS WITH POISONS. 

The use of poisons is generally the first measure suggested for the 
destruction of an injurious insect, and experiments along this line 
were begun by the senior author early in the course of liis investiga- 
tions. An appreciation of the salient features in the Ufe liistory of 
the pest soon emphasized the f utiUty of using a poison which would 
destroy the workers only. Any poison, to affect the rate of produc- 
tion or to exterminate the species, must be one wliich wiU destroy the 
fertile queens and the immature stages, all of wliich are located within 
the nest and are suppUed with food by the workers. 

No way could be devised by wliich poison could be administered to 
the queens and larvae except by having the workers carry it to them 
from sources of supply outside the nest itself. The problem therefore 
resolved itself into the search for some poison which would be fatal, 
but which at the same time would act so slowly within the workers' 
stomachs that they could transport it to the colony and there feed it 
to the inmates before perisliing themselves. 

Some small measure of success attended our experiments in this 
Hnebut, incidentally, another and much more valuable use for poison- 
ous mixtures was discovered. 

Arsenate of lead, containing but Uttle arsenic in soluble form, 
naturally suggested itself as the most promising substance for the 
purpose. Accordingly it was tried in various experiments, of wliich 
the following will serve to illustrate the results obtained : 

A mixture was made of 1 part pulverized sugar, 1 part paste 
arsenate of lead, and 2 parts of honey. The ants carried this away 
rapidly and on August 1 1 exhausted the entire amount that had been 
put out. The supply was renewed, but on August 12 it remained 
untouched. An examination of the nest was then made and it was 
found to be entirely deserted; the colony had moved away, taking 
with it aU immature stages. That tliis action had been taken to get 
outside the sphere of danger from the poison there can be little doubt, 
for this colony had occupied the same spot for many weeks, despite 
the fact that it had been frequently dug open for examination and 



METHODS OF REPRESSION. 85 

had been entirely submerged at times during hard rains. No dead 
ants were found in the empty nest; any such, if present, were taken 
away at or before the time of vacating the formicary. The ants will 
not tolerate dead wdtliin their H\dng chambers, the cadavers always 
being removed expechtiously and often to a considerable cUstance. 
This makes it extremely cUfficult to tell, by examination of a colony 
in nature, how many of the individuals have been killed by any poison 
fed to the workers. The action of the colony in moving outside the 
zone of danger was observed in many subsequent experiments in 
wliich poisoned food was used, and tliis gave us the clue to the use of 
sweetened arsenical mixtures as repellents for driving the colonies 
away from infested situations. The same phenomenon, improperly 
understood, has been responsible for the conclusion, arrived at by 
several experimenters, that the use of such mixtures was actually 
exterminating the ants, their absence after use of the poison being 
ascribed to their death and not to their migration to a safer place. 

That the mixtures containing lead arsenate, such as those just 
described, do destroy the indi\dduals wdthin the nest and that their 
continued consumption by the ants would result in extermination if 
the colony did not move away from them, were estabHshed by experi- 
ments made with colonies kept in artificial formicaries where migra- 
tion from the poison was made impossible. In one such experiment 
a small amount of the mixture last described (1 part lead arsenate 
paste, 1 part pulverized sugar, and 2 parts honey) was kept constantly 
on the food table of a colony in the formicarium. On the same table, 
but a short distance from it, food not poisoned was also kept at all 
times. The workers from tliis colony therefore had their choice 
between poisoned and nonpoisoned food. A few workers died each 
day, the larvae all succumbing a few days after inauguration of the 
experiment. At the end of about 20 days the colony seemed demor- 
aUzed and discouraged, the queen ceased to lay, and the workers did 
not work with their accustomed activity. At the end of 44 days all 
individuals were dead, the queen having hved until near the end of 
the period. 

Many solutions and mixtures containing wliite arsenic (arsenic 
trioxid) were tested in various ways and the one wliich gave by far 
the best results was made by combining one-fourth gram of arsenic 
trioxid with 20 grams of granidated sugar in 100 cc. of water.^ Wlien 
placed in a small dish anywhere witliin the foraging range of a colony 
tliis preparation would be greedily taken for a few hours, after wliich 
the ants would not touch it as long as it remained in the same position. 
Wlien the dish was moved a few feet away or placed in another part 

1 To give warning of its dangerous nature it is well to add to this niLxture sufficient confectioner's color 
paste to dye it a brilliant red or green. Fruit juices, as of raspberry or similar fruits, may be added to 
accomplisli tlie same end. 



86 THE ARGENTINE ANT. 

of the same room and ''rediscovered" by the workers they seemed not 
to recognize its dangerous nature and would take it as before. After 
a few experiences of tliis kind the colony would move away from the 
vicinity. Only in rare instances were these migrations actually wit- 
nessed, as they seemed usually to take place during the night. A 
solution containing more than one-fourth of 1 per cent of arsenic did 
not give as good results for, in such cases, many of the workers died 
wliile sipping up the poison or on their way to the colony. Thus the 
poisonous nature of the substance was more quickly detected by the 
ants and work on it was stopped proportionately sooner. In all cases 
the ants removed the dead and dying from along their trails and from 
the vicinity of the poisoned mixture. 

A number of experiments were made to determine whether or not 
the ants could distinguish between poisoned and nonpoisoned foods, 
with the result that they evidently could not do so; this perhaps being 
the reason that they moved their colonies away from the vicinity. 
One of these experiments was as follows: 

On July 9 a fruit jar containing honey was placed on the floor of a 
small shed, where the ants had been very abundant for weeks. By 
the following day all honey had been removed by the workers and more 
was placed in the jar. Between the 9th and the 12th the jar was 
replenished several times, the ants during tliis time carr3ring away 
more than a half pint of honey. At noon on July 12 a small glass 
vessel containing a mixture composed of one-half of 1 per cent of 
arsenic and 20 per cent of sugar was placed about 3 inches from the 
honey jar. The ants commenced taking tliis solution at once, and 
in the course of five minutes the vessel was black with them. At 4 
p. m. on the same day they were stiU working with undiminished 
vigor on both the honey and the poisoned solution. At 8 a. m. on 
July 13 there were only about one-fourth as many ants visiting the 
jars as on the previous day. They were still worldng on both the 
honey and the solution and many dead ants lay about. At noon of 
the same day very few were visiting the vessels, but many were 
engaged in carrjang away the dead bodies of their erstwhile sisters. 
A few were still taking the arsenic solution, but it was e^^dent that the 
ants did not know wliich of the food supplies was destroying them. 
At 2 p. m. on July 14 only two workers were in the vicinity of the ves- 
sels and neither of these was feecUng. On July 15 all ants, both ahve 
and dead, were gone, and not a single worker could be found in the 
builcUng. Plenty of the nonpoisoned honey still remained in the jar. 
On July 16 and 17, also, no ants were to be found in the shed, even 
though heavy rainstorms in the meantime drove them indoors in 
many other buildings and decreased their available outdoor food sup- 
pily. Tliis experiment and many others demonstrated not only the 
effect of the poison in driving the ants from the vicinity, but also that 



METHODS OF EEPKESSION. 87 

food supplies could be protected merely by having tlie poison near 
them. In practical work it was found that the placing of two or tliree 
saucers containing a little of the arsenical solution about a room or 
under tables bearing honey, meats, etc., would effectually rid the 
vicinity of ants in from one to three days' time, and, what was more to 
the point, the ants would not return in numbers so long as the dishes 
of poison were kept there. 

CONTROL OF THE ANT IN RESIDENCES. 

No one measure will afford satisfactory reUef from tliis pest , and the 
householder who would find permanent immunity from attack must 
plan a warfare based upon an intelligent appreciation of the facts 
above set forth. Of utmost and primary importance is cleanliness. 
By tliis is meant not merely absence of cUrt in the usual sense, but 
that precautions must be taken not to leave particles of food where 
the ants can have access to them. Even crumbs of bread or cake 
left on a kitchen floor will attract the pests. Above all else fruits, 
sweets, oils, and meats must be kept where the ants can not reach 
them. The more abundant the food supply the more abundant will 
the ants become, and it has been repeatedly observed that there are 
many more colonies in residences occupied by sliiftless owners than 
in those occupied by careful housekeepers. 

Foodstuffs can not be isolated from the ants except by the use 
of repellents such as have been described, particularly ant tape. 
Tliis last should be placed around the legs of all tables, benches, 
etc., on which food supplies are kept, and the tables must not be 
allowed to touch the wall or other objects by means of wliich the 
ants can fin-d access to them. 

The corrosive sublimate tape is, of course, poisonous, and when 
there are children in the house precautions must be taken that they 
do not get hold of it. At the same time we have never known of 
a case of poisonmg resulting from its use. It is wise, also, to wash 
the hands well with soap and warm water after handling the tape. 

To assist in repeUmg the ants the sweetened arsenical mixture, 
described on page 85, contammg one-fourth of 1 per cent of arsenic, 
should be placed in small dishes or saucers m pantries and beneath 
tables, refrigerators, etc. 

Along with these repelling measures colonies of the ants should 
be destroyed at every opportunity. Hot water, kerosene, or crude 
oil can be used for destroymg every colony that is accidentally 
exposed to view by the overturning of leaves, boxes, pieces of wood 
etc. For this purpose we have found a small compressed-air sprayer, 
fiUed with kerosene or crude oil and kept in a handy place, very 
useful. Colonies nesting in the ground can be quickly destroyed 



88 THE ARGEXTIXE ANT. 

b}^ thrusting a sharp stick into the nest and pouring in a sufficient 
amount of carbon bisulphid or gasoline, afterwards closing the hole 
with damp earth. 

On most city premises the ants can be further reduced by making 
■ use of winter trap nests or trap boxes, such as are described on pages 
95-96 under the caption "Experiments with winter trap boxes." 
Mention should not be omitted at this point of the steps advocated 
by the Rev. Albert Biever, of Loyola College, New Orleans, who, 
by his constant advocacy of warfare against this pest, did much 
to enhghten the people of New Orleans concerning it. Father 
Biever's plan was to place sponges moistened with sweetened water 
in locations visited by the ants, and when these were covered with 
the pests to dip them into boilmg water. The sponges were then 
recharged and the process repeated as long as the ants would ^dsit 
them. By this persistent destruction of the workers Father Biever 
expected so to deplete the colony that not enough workers would 
remain to care for the queens and larvae and the latter would perish 
from starvation. 

A most novel way of destroying these ants was described by Mr. 
Edwyn C. Reed, of the Museo de Concepcion, Concepcion, Chile, 
in a letter to the senior author. Mr. Reed says : 

The only sure cure would be to take Biblical measures and root up the city infested, 
stone by stone, and strew it with salt. As such a radical ciu*e is not practical, we must 
be content with palliatives, and I find the following very effective: This ant is very 
fond of olive oil, and so, in sardine tins, saucers, etc., I put a little olive oil in its runs. 
The ants flock to the oil and in eating it get clogged up, so that for a spoonful of oil 
I get about that quantity of ants, dead and harmless. In practice this so weakens 
the nests that I get rid of them. . Last November I moved into a house sadly infested 
by them and at once applied the oil. They came to it by thousands and stayed 
there. In a month's time I could appreciate the result, and by the end of our southern 
summer very few were to be seen. 

CONTROL OF THE ANT IX APIARIES. 

The keeping of bees is made well-nigh impossible in sections 
heavily infested by the Argentine ant. Single colonies of the ants 
often contam more individuals than a colony of bees, and in addition 
the colonies of ants are by far the most numerous. The Argentme 
ants are not only exceedmgly fond of honey but they attack the 
bee larvae in the cells with a ferocity that is amazing. Thousands 
upon thousands of the ants will enter the hive, carrying away honey 
and attackuig the larvae. The bees themselves are unable to cope 
with such small enemies. The ants are too small for them to sting, 
and were they even to attempt picking up the ants m their mandibles 
and carrying them out of the hive they could make no appreciable 
headway against the thousands of intruders. The bees adopt what 
is perhaps the best method of defense under the circumstances, that 



Bui. 1 22, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate VII. 




Beehive on Ant-Proof Hive Stand, the Latter Resting Upon a Concrete Block. 

(Original.) 



METHODS OF EEPEESSION". 89 

of trying literally to kick out the invaders. A worker bee will rim 
in among the ants and, whirling about, will give repeated vigorous 
kicks with her hind legs, tlu-owing the ants in every direction, even 
to a distance of 10 or 12 inches. The ants are not, however, killed 
by this rough treatment, and they shortly return to the attack. 
In a few hours after the attack has commenced the bees become 
thorouglily disorganized and give up further defense, sometimes 
swarming out as a last resort. At such times the normal hum of 
the liive gives place to an entirely different note, which the expe- 
rienced bee keeper at once recognizes as that of distress. 

The difliculties of extracting and handling honey in the presence 
of these pests can be readily imagined. In order to extract we 
first scrubbed the floor of the building, usmg copious amounts of 
carbolic acid in the water. The foundations of the building and 
a space about a foot wide all around the building were then sprayed 
with crude oil. The extractor, as well as the uncapping can, was 
placed in a large iron tray containing several inches of water. When 
all these preparations were complete, the supers were taken from 
the hives, and as fast as brought in were stacked on tables the legs 
of which were wound with the corrosive sublimate ant tape. Extract- 
ing was done as exj^editiously as possible, but with all our ])ains 
the ants were all over everything before we could extract and bottle 
three or four hundred pounds of honey. Even our clothing was 
teeming with the workers and all human effort was helpless to keep 
them out of the honey. 

The number of apiaries destroyed by the ant in southern Louisiana 
has been considerable, and one of our first lines of experunental 
work was to devise some means of protecting the beehives from the 
foraging ants. Among the various schemes that were tried the 
following were found most efficient: 

Placing the hive upon a stand havmg four legs and placing each 
of these legs in a tin cup containing crude petroleum served to* deter 
the ants for a time, but rain water soon displaced the oil in the cups, 
and then with the first accumulation of dust on the water the ants 
found their way across it. This device also had the disadvantage 
of killuig all bees which attempted to crawl up the legs of the stand. 

Another device, somewhat more successful than the open cups, 
consisted of a stand the legs of which had at their tops inverted 
troughs of galvanized iron so arranged that rain water could not 
enter them, and so fixed that the ants would have to cross the troughs 
containing oil in order to reach the hive. Stands protected with 
this appliance successfully repelled all ants for about two months 
but, like the open cups of oil, resulted in the death of some bees. 

As our previous experiments had shown the repellent power of 
ant tape, already described, it occurred to us that this might be 



90 



THE AEGENTINE ANT. 



used in the construction of an "ant-proof" hive stand. Accordingly 
a four-legged hive stand was made with top and sides extending 
some distance beyond the legs and downward, so as to prevent rain 
water from reachmg the upper end of each leg. The top and sides 
were made thoroughly water-tight and the ant tape wound several 
times about the upper end of each leg. Below the tape, fitting 
snugly around the leg, was a piece of zinc about 6 inches square to 
prevent water from splashmg upward from the ground during storms. 
One of these hive stands, turned on end to show the method of 
construction, is illustrated in figure 11, and the details of construc- 
tion are further shown 
in figures 12 and 13. 
These figures are from 
drawmgs by Miss Ethel 
Hutson. The two front 
legs of the stand were 
made an inch shorter 
than the rear two to 
give proper drainage to 
the hive. In putting on 
the tape we wrapped 
about a yard of tape 
about each leg, placing 
corrosive sublimate be- 
tween the layers. Made 
in this manner these 
stands by actual test 
repelled all ants for 11 
months without any 
attention being re- 
quired except to pre- 
vent grass and weeds 
from growing up and 
touching the hive and 
upper part of the stand. 
With corrosive sub- 
limate between the 
layers of tape the latter is effective until it disintegi'ates or until it 
gets wet, and bees crawling up the legs pass the barrier of tape 
without injury or inconvenience. Our stands were made of tongue- 
and-groove lumber, which made them rather cumbersome, but there 
is no reason why such stands should not be made with top and sides 
of galvanized iron. This would make them light, durable, and 
cheap. 




Fig. 11.— Ant-proof hive stand, upturned, showing method of con- 
struction. (Senior author's illustration.) 



METHODS OF REPRESSION. 



91 



In spite of the fact that the hive stand was absohitelv ant proof 
we experienced much difficulty ia preventing grass from growing up 
under the hives and affordiag a passageway for the ants. To elimi- 
nate tliis difficulty we covered the entire apiary with about 5 inches 
of cinders and placed each hive stand upon a concrete block. (See 
Plate VII.) 

Rev. Albert Biever, S. J., devised a unique method of protectmg his 
bees from the ants. This method he describes as follows : 

Blocks of wood are obtained, upon which the legs of the bee stand rest. Then the 
cover of a lard can or large tin box sufficiently vnde when placed in an inverted posi- 
tion on top of the blocks will overlap the block of wood on all sides. A paste con- 
sisting of vaseline mixed with kerosene and red pepper is then spread thinly over 
the inside of the can or cover, and the ants will never be able to reach the legs of the 
stand and gain access to the hives. An advantage of this method is that the paste 
need not be renewed more than once every year or two, and, being protected from the 
weather, it can not be washed off. 

One can successfully keep a few colonies of bees in any portion of the 
ant-infested area by 



makmg use of the spe- 
cial stands described 
above, but eternal vig- 
ilance is the price of 
success, for when the 
ants do gain access 
to the bees the latter 
are likely to be dis- 
organized withm a 
few hours and the 
swarms will abscond. 
Along with the use of 
the ant-proof- stands one should also use every means for reducing 
the ant colonies in the vicinity of the apiary. 

The commercial apiarist can hardly continue keeping bees with 
profit after his apiary is invaded by this pest, the amount of labor in 
constructing hive stands and keeping down vegetation being almost 
prohibitive. In such cases the wisest course would be to remove the 
entire apiary to some locality where these ants do not occur. As 
already noted, the infestation is not infrequently confined to cities 
and towais, and small rural sections still free from this pest can usually 
be found within driving distance. 

CONTROL OF THE ANT IN ORANGE GROVES. 

• The main orange-growing section of Louisiana lies along the banks 
of the Mississippi River below New Orleans and extends for a distance 
of about 50 miles. This section has the reputation of producing 




Fig. 12.— Sectional view of ant-proof hive stand, showing method of 
making top and sides water-tight by *' breaking" the joints. (Sen- 
ior author's illustration. ) 



92 



THE ARGENTINE ANT. 



\\ 'IL 



ri I I 1. 



fr- — rr 



^ 






!i 



oranges of exceptionally liigli quality, and the industry has pro\^en a 
paying one for many years past. A considerable number of localities 
have during the past 15 or 20 years become infested by the Argentine 
ant, due, no doubt, to drifting logs containing ant colonies that 
lodged along the banks of the river. The warm winters, coupled with 
the presence of considerable moisture at all times, have made possible 
verj^ rapid increase of the ants, and the first result of their activities 
has been a greatly accelerated rate of increase b}^ all scale insects, and 
particularly by the chaff scale {Parlatoria pergandii Comst.). Not 
only do the ants protect this scale from its natural enemies, but they 

colonize the larvae up- 
on the young growth 
of the orange trees and 
upon trees not pre- 
viously infested. 

At times the ants 
eat into the orange 
buds, evidently in 
quest of nectar, and 
buds thus injured do 
not set fruit. This 
habit is not always 
exhibited by the ants, 
and it may be that it is 
more or less dependent 
upon the prevalence 
of scale insects on the 
trees. The secretions 
of aphides and scale 
insects are preferred 
to other food, and it 
seems not unlikely 
that when honeydew 
is abundant the buds are not molested by the ants. Wliether 
or not the ants do any other du-ect damage to the trees is still 
an unsettled question, but certain it is that the bearing qualities 
of an orchard are seriously impaired by the second season of 
infestation, the crop is almost entirely lost by the third season, 
and the trees are dying rapidly by the fourth year of infesta- 
tion. (See PL VIII.) One orchard which weU illustrates the rate 
of destruction consisted of a 20-acre tract of young grapefruit 
trees, visited by the authors in March, 1910. The trees at this 
time were about 4 to 5 feet m height and appeared very vigorous and 
healthy. The ants were, however, rapidly infesting the field from 
adjoining orchards. During the summer of 1910 the ants increased 



Fig. 13. — Sectional view of ant-proof hive stand from above, show- 
ing construction. (Senior author's ilhistration.) 



Bui. 122, Bureau of Entorrol02:y, U. S. Dept. of Agriculture. 



Plate VIII. 




Bui. 122, Bureau of Entomology, U. S. Dept of Agriculture. 



Plate IX. 




Bui. 122, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate X. 




Bui. 122, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate XI. 





Bridges which the Argentine Ant Can Not Cross. (Original.) 



METHODS OF EEPEESSION. 93 

rapidly, as did the Lecaniums, which were constantly attended by 
the ants. The o^vner sprayed industriously with whale-oil soap, but 
without apparent effect. During 1911 many of the trees died, and 
at the present time (March, 1912) the orchard is practically ruined 
and the owner has abandoned hope of saving enough trees to make the 
orchard profitable. The condition of dying trees is well illustrated 
by Plate VI, which shows a Louisiana Sweet orange tree that has been 
exposed to ant infestation for three seasons. This tree stood near the 
levee, outside the barrier ditches described below, and was exposed to 
the work of the ants. 

Another orange orchard which we have had under close observation 
has been mfested for 7 years, and durmg this time no measures have 
been taken to control the ants. In this orchard fully 60 per cent of 
the trees are dead and the remaining trees are heavily incrusted with 
both the chaff scale and the purple scale (LepidosapJies heckii Newm.). 
So abundant are the ants here that a bit of earth disturbed by one's 
foot at any point in the orchard will reveal a seething mass of ants. 
A recent crop from this orchard consisted of but 250 boxes of inferior 
quality. Other orchards, of approximately the same size but not yet 
infested by the ant, produced in the neighborhood of 3,000 boxes. 
At Soccola Canal there is a small tract of land on which four orange 
orchards have been planted in succession, all of which have died before 
reaching bearing age. The entire neighborhood is heavily infested, 
and Mr. S. M. O'Brien, of Nairn, La., states that to his knowledge the 
ants have been abundant at Soccola for at least 17 years. The plat 
has now been entirely abandoned as an orange grove, the last of the 
dead orchards having been removed during 1911 and the land devoted 
to the growmg of truck crops. 

METHOD OP DISSEMINATION IN THE ORANGE SECTION. 

As already indicated, the most probable sources of original infesta- 
tions in the orange section were drifting logs in the river, these logs 
carrymg living colonies of the Argentme ant. In times of flood these 
logs are thrown up on the batture (the space between the river bank 
and the levee) and remain there in large numbers. It is the history 
of practically aU infestations in this section that the ants first appeared 
on the batture, then along the levee, and from the latter worked their 
way back from the river. At all the infested points the levee is found 
to be teeming with the ants and the batture itself is a constant breed- 
ing place. A portion of the infested batture, covered with a thick 
growth of willows, is showai in Plate IX. Here the ant colonies are 
found under every particle of driftwood and trash, and during almost 
the entire year they are in attendance upon Coccidee and Aphididae 
on the willows. For a number of weeks each year this batture is 
covered with several feet of water from the river, but the infestation 



94 THE ARGENTINE ANT. 

seems not to be lessened thereby. During flood time many of the ant 
colonies migrate to the levee adjoining, while still others ascend the 
trees out of the water's way. Curious nests or sheds, constructed 
by the ants from particles of earth and trash, are of common occur- 
rence in the tops of the willow trees. 

In some few places it is evident that the railroad has been the means 
of introduction, the infestation having started at points on the railroad 
where considerable merchandise from New Orleans was constantly 
being unloaded. 

EXPERIMENTS IN THE ORANGE GROVES. 

The writers' first experiments with the pest in orange groves were 
commenced in the spring of 1910. At that time only one grower in 
the Louisiana orange section was attempting anything like a system- 
atic campaign against the ants. This grower had adopted a novel 
and rather effective method of destroying them. The infested por- 
tion of his orchard ijnmediately adjoined the levee and, as is usual 
with land along the river, was lower by several feet than the water in 
the river during flood stages. The water could therefore be siphoned 
over the levee to the orchard as rapidly as needed. (See PL X.) To 
prevent the spread of the ants to additional territory the infested 
block had been surrounded by a ditch, a section of which may also be 
seen m Plate X, in which water was kept at all times. During flood 
stages of the river the water was siphoned over for the ditches at small 
expense and through the ditch system drained away to the swamp in 
the rear of the plantation. At other times the water was kept in the 
"ant ditches" by use of a gasoline engine and pump installed on the 
levee, as shown in Plate X. It was, of course, necessary to take pre- 
cautions that the ants should not find accidental and artificial means 
of crossing the ditches. Permanent bridges for the passage of teams 
could not be*left, so a swinging bridge which could be lifted when not 
in use was devised. The ditching system for preventing spread of the 
ants was shortly adopted by many other growers, some of whom used 
an ingenious divided bridge (PI. XI) which could be crossed readily 
by teams, but which had a 2-inch crack through the middle that effec- 
tually prevented the passage of the ants. 

The grower referred to had put in practice the following method of 
destroying the ants: A small levee or ridge was made around the 
infested block of trees. Water was then admitted through the siphon 
from the river until the ground in the block was entirely covered. As 
the water slowly rose the colonies of ants moved up into the orange 
trees. Then the water was drawn off and the ants, descending, found 
the ground still too wet to live in, whereupon they migrated en masse 
to the surrounding small levee. The water was then turned on for 
the second time to keep the ants on this ridge, and here they were 



METHODS OF REPRESSION. 95 

destroyed by exposing the colonies with a shovel and scaldmg them 
with hot water or spraying them with kerosene. At the senior 
author's suggestion a number of small boxes filled with hay and trash 
were placed at various points in the orchard. Wlien the water was 
admitted it was found that the colonies moved into these boxes in 
preference to going up the trees. They could thus be destroyed with 
one flooding instead of two, as formerly. 

It may be remarked in passing that the ditches, when pains have 
been taken to prevent the ants crossing them, have effectively limited 
the spread of the ants through the groves. This fact amply substan- 
tiates our observations, mentioned on pages 19-20, to the effect that 
colonies are never established by individual queens returning from a 
marriage flight. Were colonies established in this manner, the areas 
of infestation would not be sharply defined, nor would ditches retard 
the dispersion of the ants from heavily infested centers. 

EXPERIMENTS WITH WINTER TRAP BOXES. 

The success which had followed experiments at Baton Rouge in 
getting the ant colonies to concentrate during the winter in boxes 
of decaying vegetable matter induced us to try the same plan in 
an infested orange grove. Accordingly in November, 1910, a large 
number of boxes, each 2 by 2 by 3 feet, of rough lumber, were made 
and distributed throughout the infested block. Each was filled, 
during the latter part of October, with a mixture of cotton seed and 
dead grass. The top of each box was left exposed to the weather, 
so that rain would enter to moisten the contents and start decay. 
An examination of the boxes on November 16 showed that many 
colonies had entered them, but that many still remained in the 
ground. To afford the ants less natural protection the orchard was 
cultivated to remove the standing grass and weeds. In January, 
1911, the authors again visited this orchard and found all boxes 
filled almost to overflowing with enormous ant colonies. Each box 
contained workers by the hundreds of thousands and queens by the 
hundreds. A close examination in various parts of the orchard 
showed, however, that not all colonies had entered the boxes. Some 
few colonies had remained in their underground nests, particularly 
where grass or weeds had been overlooked in the November cultiva- 
tion and where, therefore, these colonies were afforded more protec- 
tion than in the plowed portions. Whether the already crowded 
condition of the boxes had prevented other colonies from entering 
them we could not determine. 

Experiments were now undertaken in destruction of the colonies 
in the boxes. Metal covers had already been constructed for con- 
fining gases in the trap boxes. (See PL XII.) Experiments were 



96 THE AKGENTINE ANT. 

first made in fumigating the boxes with hydrocyanic-acid gas (see 
pp. 82-83), but these were not successful. Carbon bisulphid was next 
tried, with perfect success. Delay in obtaining a sufficient supply 
of bisulphid resulted in delayed treatment of many of the boxes, 
and doubtless some of the colonies escaped as the weather became 
warmer in the early part of February. Nevertheless, the number 
of queens and workers destroyed ranged into the millions. The 
owner wished to deal the ants the hardest blow possilple, so early 
in the spring he flooded the orcharfl, drove the remaining ant colo- 
nies to the boxes, and fumigated these the second time. 

The results of this work were eminently satisfactory. The orchard 
was first infested by the ants in 1909. In 1910 they reached enor- 
mous numbers; chaff and purple scales increased until the trees were 
almost encrusted, and many of the trees showed signs of failing. 
The foliage began to turn yellow, and the crop of 1910 fell off 
severely, in spite of the flooding that was done by the owner in the 
spring of 1910. During the summer of 1911, following the use of 
the trap boxes, the orchard improved remarkably, and the crop was 
up to the original production. It was found that when the boxes 
were left in the orchard ant colonies took up their abode therein 
during the summer months; for this reason these boxes were fumi- 
gated with bisulphid from time to time. An examination of the 
orchard in January, 1912, showed that the infestation by the chaff 
scale had been greatly reduced by diminution of the ants, even 
though the owner had done no spraying for destruction of the scale 
insects. The ant infestation showed some increase in the autumn 
of 1911, but the orchard had returned to its normal healthy condi- 
tion, and it was evident that a continuation of these methods would 
insure good crops indefinitely. A view of this orchard, taken in 
January, 1912, is shown in Plate XIII. 

One important point came to light in these experiments, and that 
was the necessity of placing the trap boxes in position early in the 
autumn so that the vegetation in them would be decaying weU at 
the approach of cool weather in November. With considerable 
decomposition going on at the time the ants are seeking winter 
quarters, the warmth of the box becomes very attractive to them. 

The .use of arsenicals and other poisons in the infested orange 
groves was found impossible, for the reason that the secretions of 
scale insects and aphides are preferred by the ants to aU other foods. 



Bui. 122, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate XII. 




Bui. 122, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate XIII. 




BIBLIOGEAPHY. , 97 

BIBLIOGRAPHY. 

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1907. Martins, M. N. — line fourmi terrible envahissant I'Europe (Iridomyrmex 

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Ent., vol. 2, no. 2, pp. 174-192, figs. 1-4, plates 5-7, April. 

1909. Newell, Wilmon, and Rosenfeld, Arthur H. — Some insects injurious to 
truck crops. <Cir. 27, La. State Crop Pest Comm., pp. 112-116, 126, July. 

1909. Newell, Wilmon. — Measures suggested against the Argentine ant as a house- 
hold pe8t.<Joum. Econ. Ent., vol. 2, no. 5, pp. 324-332, fig. 1, pi. 1, October. 
75508°— Bull. 122—13 7 



98 THE ARGENTINE ANT. 

1909. LouNSBURY, Chas. p. — Destruction of Houtkapper white ants.<^Agr. Journ., 
Cape Town, July. (Mention of ineffective measure against Iridomyrmex 
humilis.) 

1909. LouNSBURY, Chas. P. — -Report of the Government Entomologist for 1908. 
Cape Town, S. Afr., pp. 66-68. 

1909. Newell, Wilmon.— 3d Bien Rept. La. State Crop Pest Comm. for 1908-1909, 

pp. 4-5, December. 

1910. LouNSBURY, Chas. P. — Report of the Government Entomologist for 1909. 

Cape Town, S. Afr., pp. 90-91. 
1910. Smith, John B. — Insects and entomologists: Thek relation to the community 

at large. <Pop. Sci. Monthl., vol. 76, no. 3, p. 221, March. 
1910. Dean, W. Harper. — Some notes upon the life history and habits of the sorghum 

midge, Contarinia (Diplosis) sorghicola Coq.<Journ. Econ. Ent., vol. 3, 

no. 3, pp. 205-207, April. 
1910. RosENFELD, Arthur H. — lusects notably injurious in Louisiana during 1908 

and 1909.<Journ. Econ. Ent., vol. 3, no. 2, p. 213. 
1910. Wheeler, Wm. M. — Ants, their structure, development and behavior. New 

York, pp. 663, figs. 286, and plates. Iridomyrmex humilis, pp. 153, 154, 155, 

233, 542. 
1910. Garrett, J. B.— A preliminary report on the sugar-cane mealy-bug. <Bul. 

121, La. Agr. Exp. Sta., p. 10, July. 
1910. Sajo, Karl. — Die argentinische ameise, eine neue sechsfussize Grossmacht. 

<Proraetheus, Jahrg. 21, pp. 634-638, 1 fig. 
1910. Sajo, Karl.— Une invasion de fourmis.<Prometheus, p. 634. Reviewed in 

Revue Scientifique, Paris, p. 309, September 3. 
1910. Barber, T. C— The Coccidae of Audubon Park, New Orleans, La.<Journ. 

Econ. Ent., vol. 3, no. 5, p. 423, October. 

1910. WooDWORTH, C. W.— The control of the Argentine ant.<Bul. 207, Cal. Agr. 

Exp. Sta., Berkeley, Cal., pp. 20, figs. 28, October. 

1911. Dean, W. Harper.— The sorghum midge. <Bul. 85, part 4 (revised). Bur. 

Ent., U. S. Dept. Agr., p. 57. 
1911. Nickels, L. J. — Field work in the control of the Argentine ant.<Journ. Econ. 

Ent., vol. 4, no. 4, pp. 353-358. 
1911. Newell, Wilmon.— Practical information for beginners in beekeeping. <Bul. 

142, Tex. Agr. Exp. Sta., p. 37, December. 



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